(4). Wherever pressure is taken off water which is above the boiling point a sudden generation of This has been actually obsteam must ensure.

inte a voltaic circuit a resistance varying off; (D) engine running feed going on. Separate
exactly as the plate or membrane vibrates. observations were taken with three different de-
The current flowing along the line being scriptions of feed apparatus-viz, an injector, a
exactly as the total resistance of the circuit, plunger pump, and two plunger pumps combined.
S parate series of observations were also taken
it follows that the current passing at any when the pressure was rising, and again when it
point in the line varies as the membrane or
was falling.
plate vibrates. These currents passing through
the coils of a suitable electro-magnet, per-
manent magnet with coils, or polarised electro-
magnet, excite, in an armature which takes
the form of a plate, vibrations which correspond
with those of the membrane or plate of the
sending station; but the vibrations of the
plate at the receiving station can be heightened
at will by the introduction of an increased
battery power in the circuit. This effect is
obtained by means of a circuit metallic plate
held by a collar against a disc which is per-
forated by the mouthpiece. The plate is free
to vibrate in a manner similar to a drumhead,
and carries at its centre a light stud, which is
covered with platinum. A fine screw is so
placed working in a rigid standard that its
platinum-covered end can be brought into
contact with the stud above mentioned, or
receded from it at will, the distance between
the screw and the stud being capable of fine
adjustment. The metal standard, in which the
Derew works, is connected with a terminal
screw, to which the line wire is attached, whilst
the metallic plate, and with it the stud, are
(4). Where the feed was effected by an injector
placed in connection with a terminal screw, to these differences were least, not exceeding 7°; with
which one pole of a battery is connected, the a single pump they amounted in some cases to 9,
other pole of which is to earth or return wire. ing to a difference of pressure of 2 atmospheres
and with two pumps to as much as 1740, correspond-
In order to work the instrument a drop of a (about 35lb.).
fluid or semi-fluid substance, or a flame such as
to be an imperfect conductor, but to be as
little as possible liable to electrolytic action, is
placed between the end of the screw and the
stad, and the screw is made almost to touch
the stud. On speaking into the mouthpiece,
as the plate vibrates to the tones of the voice,
the distance between the end of the screw and
the stud varies with each vibration, and as the
distance varies so does the resistance offered by
the drop of fluid substance between the contact
points vary. With the varying resistance a
varying current passes along the line. This
vibrating current is received at the distant
station on an electro-magnet, or permanent
magnet coiled, or on a polarised electro-magnet,
and there operates by the varying attraction of
a thin iron plate or diaphragm placed in front
of it.

served in the experiments to take place to the
amount of atmo-phere under ordinary conditions.
In exceptional cases it might be much greater,
especially when the large diff rnces of pressure at
The pressure as given by the gauge in every case different parts of the builer (sometimes amounting
differed from the theoretical pres-ure deduced from to 3015.) are taken into account. The sudden
the temperatures. As these latter always varied spring of the pressure gauge at the opening and
among themselves exact agreement was of course shutting of the regulator indicates the vio eat effects
impossible; but this was not enough to account for which rapid changes of this kid would produce in
the differences observed, which may possibly be a mass of vapour at high tension. The author
attributed to defects of the gauge, but should rather thus considers himself to have shown that under
be taken into account among the general results of a rare but not impossible combination of unfavour-
the experiments. These are as follows:-
able circumstances, a sudden generation of steam
(1). When the feed was shut off, whether the might occur violent enough to burst, if not a new
engine was standing or running, the thermometers boiler, at any rate one deteriorated by long working.
at the fire-box and in the middle of the boiler gave
At the same time the much slighter effects of this
very nearly equal readings. At the smoke-box end kind produced by an injector, as compared with a
the temperature was somewhat lower, but the dif- feed-pump, sheuld be noted as forming a substantial
ference was not above 5o.
advantage on the side of the former.

(2) With the feed shut off, but with rising temperature and pressure, the indicated tension of steam in the steam space was about 0-2 atmosphere THE COMPOSITION AND WORKING OF (3b.), higher than the theoretical pressure at the and pressure it was about as much lower. hottest part of the water: with falling temperature

EXPERIMENTS RELATING TO BOILER

EXPLOSIONS.

In publishtitution Civil N the abstracts of papers published in the foreign Engineers, there is a useful article by Dr. Hermann Scheffler, from a perusal of which we find that the author is disposed to refer many boiler explosions to the creation of a marked disproportion between the external pressure acting on the boiler water and internal temperature. This may act in two ways: (1) as a primary cause of explosion where the taking off of the pressure produces a sudden and violent generation of steam, the shock of which is greater than the boiler can withstand; (2) as a Becondary cause where a rent in the boiler prodaced by some other means creates the disproportion, and the ensuing generation of steam comes in to render the explosion much more violent and deatractive. The second fact is generally admitted, but as to the former there are great differences of opinion, and it is therefore desirable that the point abould be cleared up by actual observation on the actuations of pressure and temperature occurring within st am-boilers under various circumstances. With this view Dr. Scheffler affixed three thermoeters (made specially for the purpose by Messrs. Schaeffer and Budenberg) to different parts of the Boiler of a locomotive-viz., one in the front of the beiler, close to the entry of the feed-pipe, and therefore where the lowest temperature might be Booked for; the second about the middle of the length of the fire tubes, where the temperature would probably be highest; and the third in the front of the fire box and near its top. A large series of observations were taken of these thermometers by competent persons, and at short intervals. The results are embodied in a table, which gives for each observation (1) the actual pressure at the moment 39 given by the pressure gauge, in atmospheres; (2) the readings of each of the three thermometers; (3) the theoretical pressure of steam corresponding to esek of these temperatures, as calculated by the formula of Regnault. The observations fall into four groups according to the following condition: (a) engine standing, feed shut off; (B) engine stand. ing, feed going on; (c) engine running, feed shut

(3). When the feed was opened the temperatures at the three places fe'l unequally; the fall being small in the middle, greater at the fire-box, and greatest at the smoke-box near the entry of the feed-pipe.

(5. A fall in the temperature of the water was in
all cases followed by a fall in the tension of the
steam; but when the cooling was rapid this fall
was less in proportion to it, so that the actual
tension became higher than the theoretical pressure
ference so observed amounted to 2 atmospheres.
at the points of observation. The greatest dif-

(6). While this held in general, there were cases
where, at the commencement of the feed, the
theoretical pre sure at the hottest point was for a
short period higher than the actual steam tension,
the greatest difference, however, not exceeding 0 43
atmosphere.

(7). When the injector was used the temperature of the feed-water, immediately before entering the boiler, was from 40° to 60° higher than that of the tender-water. This, of course, accounts for the inequalities of pressure produced by an injector being much smaller than by a pump..

ALLOYS.-V.*

WHEN putting fresh fuel into the furnace after few pieces of large coke should always be laid on a crucible has been charged with metal, a top of it, so as to concentrate the heat upos the

I

metal. Crucibles of all sizes can be obtained from

the manufacturers, and small ones from any drug store; but where it is impossible to purchase cruci have had to do on several occasions when making where it was impossible to obtain crucibles. In assays of different minerals in parts of the country making a crucible the first thing necessary is to procure a white, tenacious, plastic clay, which will stand the fire without melting; a good fireclay mixed with about one-half coarse sand, will make a good crucible; but where fireclay cannot be obtained we must use some other clay, which should be mixed with some old firebricks finely broken up; and if they cannot be obtained, then pieces of porcelain, Chinese ware, or common stoneware may be broken articles can be obtained, then quartz rock or sandup and used with the common clay. If none of these stone may be used. They should be heated to redness and suddenly cooled by throwing into cold sand and mixed with just enough clay to make it water, after which they are broken up into a coarse adhere together. Too small a per cent, of clay bas

bles, the founder often has to manufacture them, as

a

tendency to weaken the crucible, and too large a The mixture of sand and clay must be well worked quantity makes it liable to crack when heated. (8). A sudden opening or closing of the regulator When forming the crucible a wood block of the with the hands before moulding it into the crucible. produced an instant fall or rise of the pressure gauge desired shape may be used for a pattern, and the of about 3lb., or 1lb. respectively, followed in crucible formed by coating the mixture on to the general by a slight recoil towards the original stand-block and allowing it to get partially dry before re

point

(9). The opening of the regulator caused a rapid highest, and a rise of that which stood lowest, fall of the thermometer which at that moment stood amounting in each case to about 33, thus producing an equalisation of temperature to the amount of about 7°.

moving the block. When it is desirable to make small crucibles a good-shaped glass tumbler may be od used for a pattern, and the mixture coated either on crucible desired. To prevent the mixture from sticking to the pattern the pattern may be covered with paper before applying the mixture. The bottom of The following general conclusions are drawn from the crucible should always be a little thicker than the above facts by the writer:-(1). The supply the sides. When a crucible has been formed it of water by feed-pump causes large variations of should be allowed a few days to dry in the sun or in temperature in the different parts of a boiler. These a gentle heat, as it takes some time for the water to act on the steam tension, but with the general re-evaporate from the clay. When the crucible has sult that this tension is decidedly in excess of the been sufficiently dried it is then baked or exposed to theoretical pressure due to the water temperature: a strong red beat. The baking may be done is s thus fortunately tending to retard, and not to common cook stove oven or in an open fire. When accelerate, the generation of steam. baked in an open fire the crucible should be set in the centre of the fire, and the fuel, either wood or coal, plied all round it, so bas to heat it evenly and prevent breakage. After it is sufficiently baked it should be covered over with the hot ashes to protect it from the sudden rush of cold air which will follow the exhaustion of the fire. If it is desirable to have a cover for the crucible some small slabs may be made of clay and burned with the crucible.

(2). At the first moment of opening the feed the converse is observed, the steam tension being about 04 atmosphere in defect of the theoretical pressure. The same holds to a smaller extent when the feed is shut off, provided the temperature and pressure are falling at the time.

The explanation of the above facts is obvious. When the pressure is lessened by the steady abstraction of steam it falls steadily both in the water and the steam space. When the abstract on is rapid (as with steam blowing off) the water maintains for a time a higher temperature than the steam space, with a corresponding generation of steam. When the pressure is lessened by actual cooling of the water, the steain only follows it gradua ly, and keeps up for a time a higher tension. The slight converse effect, at the moment of opening the feed, is accounted for by the additional consumption of steam due to the feed-pump, and perhaps by a slight condensation of steam effected by the first entry of the cold water.

(3). When he temperature and pressure are rising instead of falling, the steam tension will similarly appear in excess or in defect of the theoretical pressure, according as the original cause of the rise is a checked consumption of steam or a more rapid generation. The first case is shown in the experiments when the engine was standing, the second on several occasions when it was in motion.

Cupel.

The cupel is a small flat cup resembling the bottom of a crucible. It is generally from 2in. to 4in. in diameter, and from in. to Hin. deep, with a flat bottom. It is generally used for refining gold and silver, and is sometimes used by jewellers in forming alloys and melting metals. The cupel is made of finely pulverised bone ashes and wood asbes mixed together. In forming the cupel the white bone and wood ashes must be we'l pulv rised and siited, and only as much water mixed with them as will cause them to adbere slightly. Care must be taken to not use too much or too litt e water, for extremes either way are equally injurious. The ashes should be pressed into the desired shape, and a strong pressure brought to bear up on them to unite them properly. The fresh cupels are then air dried, which may be done in the sun or on the top of s

* From a series of articles by Mr. E. KIRK, published in the Iron Age.

stove. After they are thoroughly dried they are ready for ne. Without baking or burning the capel is easily broken and requires gentle handling. Blowpipe.

are separated by a loose iron plate. The hood or mouth of the stack is suspended from the ceiling over the hearth with counterpoise weights, so that it may be raised or lowered, according to the magnitude of the work. The common blacksmith's The blowpipe and an alcohol lamp are largely used forge fire is frequently used for brazing: It is in hard soldering, tempering small tools, and by temporarily converted into a brazier's hearth by chemists and mineralogists as an important means being built hollow around the fire, and the fire of analysis, &c., and for these uses the blow-removed from the wall or flue, out into the centre pipe has received very great attention, both from of the hearth. But the brazing operation injures mechanics and distinguished philosophers. Most the fuel so that it cannot be again used for ordinary of the small blowpipes are supplied with air forging of iron or steel. For want of either the from the lungs of the operator, and the larger brazier's hearth or the blacksmith's forge, the ones, or where the blowpipe is brought into general ordinary grate may be used, or it is better to employ use, it is supplied with air from a bellows a brazier or chafing dish containing charcoal, and moved with the foot or from a vessel in which the the fire urged with a hand-bellows, which should air has been condensed by a syrings, or from a be blown by an assistant, so that the operator may small rotary fan. The ordinary blowpipe is a light have both hands at liberty to manage the work and brass or tin tube about 10 or 12 inches long, and fuel. The best fuel for brazing is_charcoal, but fromto of an inch in diameter at the end for the coke or cinders are generally used. Fresh coals are mouth, and 1-16th or less at the jet end. The small highly injurious to the work, on account of the end is slightly curved, so that the flame may be sulphur they contain, and soft or bituminous coal thrown immediately under the observation of the cannot be used at all until it is well charred or conoperator. There are several other kinds of blow-verted into cinders. Lead is equally as injurious pipes for the mouth, which are fitted with various in the fire for brazing as for welding iron and steel, contrivances, such as a series of apertures of different or in forging gold, silver, or copper, for the lead is diameters, joints for portability and for placing the oxidised and attaches it-elf to the metals that are jet at different arg'es, and with a ball for collect- being brazed or welded, and prevents the uniting of ing the condensed vapour from the lunge; but none the metals, and in all cases it renders the metal of these are in common use. The blowpipe may be brittle and unserviceable. There are many kinds of supplied with air from the lungs with much more work which require the application of heat having effect than might be expected, and, with a little the intensity of the forge fire or the furnace, but in practice, a constant stream can be maintained for many of these cases it is only desirable to heat a several minutes if the cheeks of the operator are small portion of the work, and avoid soiling the surkept fully distended with wind, so that their face of the remainder, and also to have the work elasticity alone will serve to impel a part of the air, under the observation and guidance of the operator, while the ordinary breathing is carried on through as in brazing or soldering small articles of jewellery, the nostrils for a fresh supply. silver plate, &c. In these cases the blowpipe and pointed flame is generally used, and in many cases the work is supported upon charcoal so as to concentrate the heat upon it.

The beat created by the blowpipe is so intense that fragments of almost all the metals may be melted when they are supported upon charcoal, with the heat from a common tallow or wax caudle. The most intense heat from the blowpipe is the pointed flame, and the hottest part of the flame is the extreme point of the inner or blue flame. Large particles of ore or metals that require less heat are held somewhat nearer to the candle or lamp, so as I to receive a greater portion of the flame, and when a very mild degree of heat is wanted on a small piece of metal it is held further away. By thus increasing or decreasing the distance between the candle or lamp and the object to be melted, any desirable degree of heat may be obtained. When only a minute portion of metal is to be heated the pointed fame is used with a mild blast; but when it is desirable to heat a large surface of metal, as in soldering and brazing, a much larger flame is used. This is produced by using a lamp with a large wick, plentifully supplied with oil, which produces a large fame. The blowpipe used has a larger opening than the one used for the pointed flame, and it is held a little distance from the flame and blown vigorously, so as to spread it out over a large surface of the work. This is called the bush or sheet flame. The work to be brazed or soldered by this flame is generally supported upon charcoal.

When melting metals with the blowpipe, the metal to be melted is laid upon a flat piece of charcoal, which has previously been scooped out slightly hollow in the centre to prevent the metal from ruuning off when melted. If it is desirable to run the metal into a mould when melted, a small groove or lip is cut in the charcoal, and when the metal is sufficiently beated it is poured into the mould. In this way the jewellers melt most of their gold, silver, &c., when making rings and other jewellery. The cupel is also used for melting metals in with the blowpipe, but it is net so good as the charcoal, for it is liable to break from being heated unevenly and spill the metals. There are several different kinds of stationary or bench blowpipes used by jewellers, braziers, &c.; but as they are not much used in the art of founding I shall not describe them in this work.

Braziers' Hearth.

A NEW MICROMETER.*

T is not every microscopist who can afford a

like a camera lucida set backwards. But just then I had occasion to investigate for another purpose the theory of the apparent distance of the magnified object. I found that as the focus is altered, as the plane of the image varies from the nearest limit of distinct vision to infinite di tance. Then why not dispense with the lens altogether, and compare the reflection of the scale itself with the object, adjusting its distance till the divisions on it coincide with those on the stage micrometer? At first it seemed as if it would be hard to compare the reflection of s real scale with an optical image, but it soon proved otherwise. Just as in the camera lucida you see the image of the object thrown on the paper, and may measure it upon a scale drawn there, so here you see the reflection of the scale in the field of the miccoscope, and may compare it with the object. This, then, is the principle of the new micrometer. Briefly, it is an inverse application of the camera lucida, coupled with the direct use of a scale, the gradua tions of which are adjusted to size by varying its distance from the eyepiece.

In its simplest form, which I prefer, the instrament consists of a cap, A, slipping over the eyepiece, and carrying an arm, B, on which slides a clip, C, to bold the scale, D. The reflection of this scale is thrown into the eye by the diagonal glass, E, and compared with the object seen at the same time through the eyepiece, F. It may be objected that this is a heavy side strain for the tube. Practically I have not found it eo, but the stem may be brought parallel with the tube by using a second larger mirror of looking-glass as in the second figure, or, the whole thing may be made smaller by having a lens to form the image of the scale. But then the instrument loses its simplicity, and is not easy to use.

The stem should be about 10 inches long, and should be made to unscrew. Then, as to the reflector, I find thin cover glass gives a double image. Sömmering's steel disc, the camera lucida, or Dr. Beale's neutral tint glass, answer equally well; bat for some purposes I should give the preference to a piece of looking glass with the amalgam scraped off in the centre. If silvered gla-s is used, a tiny drop of nitric acid from a capillary tube will eat the

thoroughly efficient micrometer, and it is not require acid very ela this case the second always that the posses or of one can find time to use image is completely overpowered by the superior it. What is wanted is a micrometer that shall (1), brilliancy of the reflection from the silvered surface. cost but little; (2), measure accurately with any The scale may be copied from any graduated rule power; (3), read in decimals of an inch or millimetre, millimetres are a convenient size-the length of without any calculation; (4), apply equally well the stem giving plenty of latitude in this respect. with all kinds of illumination; (5), and take no more It may be drawn on ivory or card. A barometer time to put on than the mere changing of an eye-scale, with its vernier, answers admirably-there piece. To invent such a micrometer is a problem being so few divisions, the eye is not confused in which I have had before me ever since the summer counting them-and it is very accurate. All but the of 1872, and I now submit to you an instrument scale itself should be blackened. For some very which bids fair to solve it. Noticing one day some brightly lit objects a transparent scale is useful, scratches on the lamp glass, focussed by the achro- while for very faint ones, or for front light, a white matic condenser, it struck me that I might use the scale on a black ground, or lines engraved on a image of a scale on glass formed in the same way as polished strip of German silver, and illuminated by a micrometer. I saw that I could easily adjust the oblique light, may be employed. This last is the best size of this image to coincide with the divisions on for star measurement with the telescope-the delicate the stage micrometer, by altering the distance silvery lines standing out with peculiar distinctness, between scale and condenser. But this was a and without interfering with faint stars. troublesome operation, until I fixed the scale in a tube sliding below the lens-and then the divisions had to be so much smaller, that with my appliances could not get them accurate. And besides it was of no use with large objects or front light, so I gave it up. However, I showed the principle, in a rough way, at a meeting of the Quekett Microscopical Club, on October 25th, 1872, and was somewhat surprised, a few months later, to find, from the paper on the " Aerial Stage-Micrometer," published in the Monthly Microscopical Journal of January, 1873, that Dr Royston-Pigott had been working in the same direction. Dr. Pigott's paper so completely detailed my principle that I determined to abandon it altogether. So I looked into the theory of the various forms of micrometer.

I

reflector may adapt the new micrometer to it. To Any one who possesses a Beale's neutral tint adjust the scale (which should be numbered with the figures reversed) so that it may read decimals of an inch or millimetre, &c, use a stage micrometer, set the instrument in position, and slide the scale along the stem nearer or farther from the eye, as it may require, till on adjusting the focus so that the apparent distance of the two images may coincide, 1-100th or 1,000th of the stage micrometer, accordevery 10th division on the scale shall cover the ing to the power used. Then mark the position of the clip on the stem with a file. This position should be found for each objective with each eyepiece; the higher the power, the more delicate is the measure The early microscopists aimed at getting micro-micrometer offers no difficulties. There is no screw ment. To the optician the construction of this meter and object in the same plane, and so laid the to make accurate in thread and in bearingobject upon the scale itself, in the lower focus of the objective. The next step was to place a real scale, microscopical scale to engrave. It is made in the In soldering or brazing large work of copper; lens, that is to say, in the upper focus of the or spider lines, in the image of the focus of the eye-way that is most convenient, and afterwards adjustod to the required standard. silver, &c., an open fire is used, called the braziers' It is easy to use. The micrometer, with its seale bearth. For large and long work this hearth is objective. Browning, in his spectroscope, employs made with a flat iron plate about 4 feet by 3, which the image of a scale in the same place. Then the clip set to the mark corresponding to the power is supported by four legs, and stands on the floor a aerial stage micrometer reversed the operation with employed, has only to be slipped on in place of the eyepiece cap, and the measurement made by inspec sufficient distance ont from the wall, so that the an image of the scale in the plane of the object, tion. If the object does not lie in the right direction, operator can get all around it. In the centre of this In the two foci of the objective all possible variations scale will revolve in the field of the microscope, eo formed in the light, before it entered the instrument. twist the clip on the stem, and the image of the plate there is a depression about 6 inches deep and of real scale or optical image had been used. But about 2 feet long by 1 wide, for containing the fuel and fire. The fire is depressed in this way so that every lens has its two conjugate foci. One focus of that it can be set exactly across the object. If the the surface of the plate may serve for the support of the eyepiece coincides with the upper one of the light is too strong to permit the scale to be seen, large work, such as long tubes, large plates, &c. objective, the other remained. It is only a virtual the lamp may be shaded with one hand, while the stage and focussing is managed with the other. The The rotary fan is commonly used for the blast. The focus, for its sign is negative. It had not been used, there is no calculation required. The stem may be tuyere iron need is similar to those used for the that I know of, except indirectly, for micrometry. marked to read fractions of an inch, a line, or a common blacksmith's forge, but with a larger open- and determined to unite an image of the scale with I wanted a novelty, so I varied all the conditions, millimetre. ing for admitting the blast to the fire. The nasal or the image of the object, after it had left the supersede the spider-line micrometer. But as far as As regards accuracy, I do not pretend that it will top of this tuyere iron, is fitted loosely into grooves, so as to admit of easy renewal, as they are burned eyepiece. At first I proposed to use the glass scale al scale micrometers are concerned, it is not inferior oat in a very short time, and must be replaced to and lens of my aerial stage micrometer, with a to any. For it will fill the field with divisions a do good work. The fire is sometimes used the full diagonal tinted reflector fixed above the eyepiece-fine and as close as can be distinguished at ten inches, length of the hearth, in which case a long or conBut it is hard to get an tinona tuyere is used. Occasionally two separate BURCH to the proceedings of the Quekett Microscopical eyepiece micrometer that reads exactly thousandthe The substance of a paper contributed by Mr. G. J. and no scale can do more. fires are used on the same hearth. In this case they Club. and even then it is only with one power.

The aerial stage micrometer, like this, has an adjustable scale, but on account of the lens being used to produce the image, any error in the setting will make five or six times the difference that it would in mine-in which the error of measurement is the same fraction of the object that the error of setting is of the length of the stem used. The personal equation, too, is evidently eliminated if the microscopist himself adjusts the setting by an accurate stage micrometer. But its principal advantage is found in the number of uses to which it may be put. When the stem is unscrewed it leaves the camera lucida intact. The clip will carry a goniometer-simply a black index, like a watch hand, with parallel sides, revolved by a button from the back in a graduated semicircle-the diameter being drawn specially broad for distinctness. It is as easy of application to a band-magnifier as it is to a microscope. I use it with my dissecting lens, and eren with my diatom-finder-a Coddington of 1-20th of an inch focus. For more than a year I have had -one fitted to my small lathe, and have rejected the ordinary gauge in its favour. The metal seems to melt away under the tool by thousandths at a time, down to the required size on the scale. My experience of it is that it would be invaluable to the optician or watchmaker; it reduces the chance of going too far, and saves a deal of time. Then with the spectroscope it is quite as easy of application, and as comfortable to use as Browning's arrangement.

BOY LABOUR IN BRITAIN AND

BELGIUM.

MR. KITSON Chambers scenenking met the Associated of Commerce meeting, recently held at Sheffield, made some remarks which have not attracted the attention they deserve. Supporting a resolution in favour of paying factory surgeons by salary instead of by fees, in the same manner and out of the same funds as factory inspectors, Mr. Kitson pointed out the practical effect of the existing system. In many of the iron and steel trades it had happened that the foremen had had to do away altogether with boy labour. In his firm they had only six boys amongst 2,000 workmen, and for that half-dozen they had to pay the doctor £5 a year. What would be the result? They would be compelled to do away with these boys in their trade. This might seem a small matter to those who inquired no further; but what would be the result to the country? Through the action of the Factory Act, several industries of the country had been already all but extinguished. Belgium was introducing into this country small sizes of rods in iron and steel, because boys could be employed in their production. All the small engines, which were at one time an important branch of English trade, were now made in France and Belgium. Mr. Kitson pointed out that by this means Parliament was extinguishing sundry trades I have already mentioned the scale engraved on in the country, and then injustice was added by seek. silver and illuminated by oblique light, as being best ing to make these trades pay the cost of their own for astronomical use. It is specially adapted for "extinguishment." Mr. Morriss, of Halifax, a reducing the brilliancy of the lines to any extent corroborated Mr. Kitson's remarks by stating tha star-spectra. - slight shading of the dark lantern director of Price's Candle Company, at Bromley,

affected than usual; but the great quantity of rain that fell during the latter part of August over a great portion of the island, accompanied as it was by the close smothering electric atmosphere, has had the effect of reducing the previously green healthy tops to a blackened mass of putrefaction that shows the silent working of the insidions parasite. We bear many large growers say that the tubers are even now so badly affected that they intend to let the whole remain in for some weeks until all that are smitten are completely decayed, as they consider that the labour of digging and repeatedly going over afterwards necessary to separate the larger propor. tion of those that are affected from the few sound, wil involve a greater outlay than the sound portion of the crop would be worth. This is anything but a bright picture, yet we fear it is not overdrawn. In gardens, where a limited space is devoted to the crop, we should urge their being taken up at once and the ground planted thickly with coleworts, winter greens, or any of the kale family. That will do something to make up, although imperfectly, for the loss of the potatoes. With a like view we would advise in all gardens, both large and small, a greater breadth than usual being planted with July sown cabbages to come in early in spring, for the extent to which potators are evidently affected in such as to make their being scarce and dear in spring a certainty.

FIC.2

than in England, although their works were
surrounded by all the mils of Lancashire. The
drift of the discussion was strongly in favour of
removing unnecessary restrictions on the employ-
ment of boy labour, and unanimously in favour of
altering the system of paying factory surgeons. It
is not for the benefit of mill-owners or manufac.
The internal diameter of a soda-water bottle-turers that the inspection is made, but for the
the contraction of the iris in a strong light-the
diameter of a dew-drop-or the sweep of a bee's
wing as it hovers over a flower-in fact any of the
thousand and one odd things that are commonly
supposed to interest the man of science, may be
determined by this simple arrangement. And I think
it not unlikely that it may prove useful to the
surgeon, in conjunction with the laryngoscope, as a
guide in preparing for an operation.

without impairing their distinctness. Nor is this his firm imported small castings from Belgium
all. Not only can this micrometer be applied to any because they could get them there more cheaply
and every kind of optical instrument, but it can be
used by itself for many things that neither carpen-
ter's rule nor callipers can reach. You have only
to fit a rod ten inches long in place of the micro-
scope tube, and set the scale ten inches from the
reflector, and you may measure the size of anything
in the plane of the end of the rod.

Dari'y the four or five years that I have had it in use I have found it so handy and useful that I determined to show it to Mr. Curties, and ask his option. He at once gave a favourable judgmentkindly offered me every assistance and encouragement, and provided one of the new micrometers for presentation to your society. I am aware that the very impcity of the instrument is prejudicial to it at Arat agat. Icere is no mystery of tubes and Jar about it to give it dignity. It looks make-shift raw than one Hot a little thought will show that it is correct in theory, and a little experience wt it w. recole al who value time and money to it appea***. And I dont not that, in abler I than . 1e, the new principle that it involves * to us, and perhaps more important

benefit of the population, and it certainly seems un-
reasonable that the cost of doing what is intended
for the good of the whole should be placed on the
shoulders of a few, and that few the very people
who are injured by the inspecting process.-
Engineer.

THE POTATO CROP.

Walculated to cause unwarranted alarm, or to
ITHOUT any wish to speak in a way
forbode worse consequences than are likely to result
from the unmistakable appearance, since our report
was made, of the potato disease throughout the
southern, western, and greater portion of the
midland counties, which we have traversed within
the last fortnight, it is with reluctance we
(Gardeners' Chronicle) come to the conclusion that
seldom, if ever, since the fell disease first appeared
in this country has the attack been so virulent.
Beginning as it did this season much earlier than
usual it was checked by the dry weather in July,
and many of us were sanguine in supposing that if
the summer had continued dry the visitation would
have been principally confined to the earliest crops,
and that the second early and latest would be less

effective little device for containing grain nickel is shown in perspective in Fig. 1, and in section in Fig. 2, in the accompanying engraving. The nickel holder consists of a flat box made of ordinary battery carbon, and having perforated sides, between which the grains of nickel are held loosely, so that the bath solution may come into contact with the entire surface of each grain. The holder is provided with a hook by which it is suspended from the battery wire. The perforated carbon plates and the strips that separate them are clamped together by rubber bolts, which are provided with milled nuts, so that the holder may be readily taken apart for cleaning, and as the top of the holder is open, the grains of nickel may at any time be readily removed for washing. This anode is practically indestructible, and we are informed by the inventor that its use insures a solid coating of metal, and effects a considerable saving in time. This invention was recently patented by Mr. Adolph C. Wenzel, of New York city, from whom further information may be obtained.Scientific American.

Artificial Production of Crystals of Silica and of the Silicates.-At one of the séances of the Academy, M. Daubrée presented a method of obtaining crystallising silica in the dry way. For this purpose the tungstate of soda is employed by M. Hautefeuille, who obtairs at will the silica crystallised either in the form of tridymite or of quartz. It has been well krown, from the researches of G. Rose, that the phosphates and the tungstates could be made to serve this purpose. But it has teen demonstrated by M. Hautefeuille that the tungstate exercises a far more energetic action in this respect than the phosphate; so that at a very moderate temperature it may be employed to reproduce a number of the more or less fusible silicates that occur in nature.

SCIENTIFIC NEWS.

THE
HE death of M. E. Quetelet, the distin-
guished director of the Brussels Obser-
vatory, is announced as having occurred at
Ixelles, on the 6th inst. The deceased professor
was born at Brussels in 1825, and was educated
at the military school as an engineer. Imme-
diately after joining the observatory, he, in
1856, published a paper on the magnetism of
the earth in North Germany and Holland,
which was followed in 1859 by one on the mag-
netic declination at Brussels, the subject of
magnetism being one that afterwards engaged
much of his time. The astronomical obser-

the L. and N. W. R., and has returned to
copper.

The use of machinery in the manufacture of
boots and shoes is rapidly driving out all but
the best hand labour. In 1877 about 100
million pairs of boots and shoes were made in
the United States, nearly a moiety of which
were sewn. The uppers, owing to the neces-
sity of human skill in judging the varying
quality of the leather in the same skin, are cut
by hand, but the soles are cut out and the boot
put together by machinery, many of the
operations being performed without the aid of
hands.

The postal telegraph officials have determined to introduce the sounder devised by Mr. Elisha Gray, of Chicago, into British offices.

large a boiler seems out of place on board a
steam vessel, and in some parts of the route
the waterpipes were burst up by the enormous
weight passing through the streets.

The authorities of Guadaloupe have offered a premium of 100,000 francs to the inventor of a process to obtain a yield of over fourteen per centum from sugar-cane. The competition is open until June 30, 1880. It is not for an improvement on sugar mills, but for the discovery of a process bearing upon the yield of turbinated sugar. All the expenses of transit, putting up of machinery or implements are to be borne by the inventor.

A very curious effect (says La Nature) is produced on oils of petroleum, even the lightest, by addition of pulverised soap-wort (a herbaceous plant of the family of Caryophile). with the oil, the latter forms a very thick The powder being digested in water and mixed mucilage, so that the vessel in which the experiment is made may be inverted without its contents escaping. What is still more singular, if a few drops of phenic acid be added, and the mucilage agitated, it becomes in a few minutes perfectly limpid.

It appears from the French Exhibition catalogue that France manufactures only about 110,000 sewing-machines annually (valued at 15 million francs), of which a third is exported. Now Singer alone manufactures about 200,000 a year. The sewing-machine appears to be poorly represented at the Paris Exhibition. Germany is absent, and America has no longer interest in forcing its exportation to Europe.

vations given in the Annales de l'Observatoire were to a large extent made by him individually, and a work to which he devoted a large A large boiler recently built by Messrs. G. part of his attention was the revision of the and R. Stephenson and Co., Newcastle, was list of variable stars. The history of the observa- removed from their works to the quay last tory from its foundation in 1833 is given in the week. The boiler weighed 60 tons, and a team biographical notice of his father, L. A. J. Quete of 52 horses was employed to drag it, and the let, the founder, in the " Annuaire" of the Bel- waggon carrying it, to the large crane on the gian Academy for 1875. The struggles against quay, whence it will be lifted into a vessel now inefficient pecuniary support had to be con-in course of construction by Messrs. Leslie. So tinued by Ernest Quetelet. His energetic efforts in connection with international meteorological service are well known, and the reputation of the Brussels Observatory for its meteorological, as well as its magnetic and astronomical work, is mainly due to his activity. A victim to science has been found in the person of Professor Fischer, of Prague. The deceased was only 25 years of age, but had already made a name as a chemist possessing more than average abilities. He seems to have imagined that he had discovered a means of The Michaelmas term of the City of London rendering cyanide of potassium harmless, and, College, Sussex Hall, Leadenhall-street, comin the presence of the storekeeper of the mences on Monday, Oct. 7. Classes are held There was 45.75 per cent. for each Bredan rifle, in French, German, and Latin, the various of sal-ammoniac and cyanide, saying that sciences, and the technology of commercial Kimk rifle, and 5:42 for each revolver. (For "science had advanced so far as to be able to life. There is a reading-room, a library, and a further data see Revue d'Artillerie, Aug.) coffee-room, with chess and draughts, the advantages of which can be obtained by students of any class, on payment of a small additional

render harmless so dangerous an agent as cyanide of potassium." He had, however, scarcely swallowed what he had tasted when he was seized with violent pains, and before a physician arrived was bezond human aid. There is no reason to suspect suicide, as the deceased was known to have been making investigations with the view of rendering cyanide harmless, and it is therefore assumed that he fell a victim to a rash experiment.

The death is also announced of Gustav Wallis, at Cuenca, Ecuador, a travelling botanist, who for nearly twenty years has been engaged by the large European horticulturists to search the little known regions of South America, and other parts, for new plants. He is said to have introduced no fewer than 1,000 new varieties, and many of the brilliant treasures of our modern conservatories are due to bis unwearied zeal and discriminating eye. He was born at Luneberg in 1830.

second volumes of a new edition of the com-
The French Academy has issued the first and
plete works of Laplace. It is a handsome
quarto, and has been produced under the editor-
ship of the permanent secretaries of the
Academy.

fee.

Mr. Hugh Clements, who frequently contributes to our columns, is about to take up Applied Mechanics, Steam and the Steam Engine, Mineralogy, Metallurgy, Nautical Astronomy, and Navigation, at the science classes held in connection with the Science and Art Department, St. Thomas, Charterhouse, E.C.; and Agriculture, Physiography, and Geology, at those to be opened at Hatfield-street Board School, Stamford-street, Blackfriars, during the ensuing session.

Statistics have recently been published of the consumption of ammunition by the Russians in their recent campaign. The total for the artillery amounts to 204,923 shots. There were consumed 10,087,344 cartridges for portable arms; the infantry using about 87.5 per cent. of the entire ammunition consumed.

From researches by MM. Bechamp and Baltas (described in last month's number of the Annales de Chimie et de Physique), it appears that certain albumens, after injection others are eliminated. In the first group are into the blood, remain in the system, while the albumen of blood serum, and the albumen of Wurtz, or triplombic albumen of egg, sexplombic albumen of the cow, and gelatine. The second group comprise the white of egg, and sexplombic albumen of egg. The way in which albumens behave in the system depends on their quality, not on their quantity. those eliminated after injection, some found in the urine without having undergone any change, others are changed in rotary power and in solubility after precipitation by alcohol. The injection of certain albumens, as gelatine and blood serum, produces more or less functional disorders, and may even cause

Another Russian scientific expedition is
about to be despatched for the purpose of
exploring the Pamir. The party, which is to
be accompanied by a Cossack escort, will
consist of Messrs. Oshanin and Nevesky,
botanists, and an officer of the topographical death.
department, named Rodionoff. On quitting
Samarcand the expedition will explore the
upper course of the river Oxus, including parts
of Afghan-Turkestan, and will return to
Tashkent via the Pamir and Ferghanah.

Of

are

It is generally recognised that the invention of the pendulum clock (so important for astronomy and other uses) dates from about the middle of the seventeenth century, but the

Although several deaths have already been announced in the papers "through eating mushrooms "the Woolhope Club will hold its annual foray on October 3, meeting at the Free Library, Hereford. Members and funguscredit of the invention has been attributed to hunters generally are requested to forward as A house in Caracas is said to have been different persons. The subject has been gone many specimens of "mushrooms" as they can nearly set on fire by the spontaneous combus- into very fully by M. Gerland (Ann. der Physik find not later than Wednesday morning, Octo- tion of a large wasps' nest in a closet under the und Chemie, No. 8, 1878), and he is led to the ber 2, in order that they may be properly roof. Although the weather was hot, the conclusion that neither Bürgi nor Treffler have arranged for the evening meeting. At present roof was tiled and covered with layers of earth, the least claim. The merit belongs to Galileo writing, we do not know how many lives are so that it is considered impossible the fire can and Huygens, who made the invention indeannually sacrificed for the want of a little have originated in any other way than by spon-pendently, but as it was made by Galileo 15 knowledge of fungi, but it must be a consider-taneous combustion. Then follows the moral: years earlier, the pendulum clock may be reable number. Through a want of knowledge Beekeepers are warned that as the normal garded as a work of Galileo's. people suffer both ways-if they let all the temperature of beehives is "very high" "toadstools" alone much valuable food is wasted; if they eat without knowledge they run serious risks.

The French Association for the Advancement of Science is to meet next year at Rheims, and at Algiers in 1881.

The American Association was not so well attended as might have been expected, the yellow fever scare keeping many from going so far south as even St. Louis, which is always a very hot place in late summer. The associa tion will meet next year at Saratoga on the last Wednesday in August, Prof. G. F. Parker being the president elect.

Mr. Webb, after an exhaustive trial, has reluctantly given up steel fire boxes for use on

(100° Fah), some chemical change may follow
à further increase of heat, which, producing
spontaneous ignition, will find suitable material
for a conflagration in the wax of the cells!

The fifty-first session of the congress of
German Naturalists and Physicians was com-
menced on Sept. 11, at Cassel, under the
presidency of Dr. Stilling. Professor Oscar
Schmidt delivered an address on "The Rela-
tions of Darwinism with Social Democracy,"
and Professor Hueter, of Griefwald, another
on the Relations of the Physicist to the
Natural Sciences." The Congress then ad-
journed to reassemble for work in the sections,
of which there are 26, representing almost
every branch of science.

It has been recently pointed out by M. Berthelot, that his small air thermometer serves for determination of low temperatures as well as of high. Where mercury thermometers can no longer be employed, because of solidification of the metal, where the alcohol thermometer furnishes only uncertain indications, by reason of the variability of the co-efficient of dilatation of this liquid, the small air thermometer gives quite correct indications. Thus, by means of it, he finds the boiling point of solid carbonic acid to be 78-2° (Regnault

779°). Chloroform is found to melt at 70°, &c.

A bed of rock-salt was recently discovered at Wyoming, in Western New York. It was struck at a depth of 1,279ft., the boring having

passed through shale, sandstone or limestone, LETTERS TO THE EDITOR.

then shale again. It had a thickness of 70ft., of which 40ft. or 50ft. consisted of pure salt. The locality is thirty miles South of Rochester, on the Rochester and State Line Railroad, and in the Onondaga salt group. It is proposed to bore on the south side of the Syracuse Valley, since there is a prospect of striking the same bed. It would be necessary to carry the boring down only a few hundred feet to settle the question. Success would substitute a mine of rock-salt of indefinite extent for weak brines.

The two rainiest regions of the United States (says Prof. Asa Gray in a recent lecture), are the Pacific Coast, north of latitude forty-five, and the north-eastern coast and borders of the Gulf of Mexico. But when one is rainy the other is comparatively rainless. For while this Pacific rainy region has only from twelve to two inches of its rain in the summer months, Florida, out of its forty to sixty, has twenty to twenty-six in summer, and only six to ten of it in the winter months.

[We do not hold ourselves responsible for the opinions of our correspondents. The Editor respectfully requests that al sommunications should be drawn up as briefly as possible.] ENGLISH MECHANIC, 31, Tavistock-street, Covent-garden, All communications should be addressed to the Editor of the

W.C.

All Cheques and Post-office Orders to be made Payable to
J. PASSMORE EDWARDS.

* In order to facilitate reference, Correspondents, when
speaking of any Letter previously inserted, will oblige by
mentioning the number of the Letter, as well as the page on
which it appears.

"I would have everyone write what he knows, and as only, but in all other subjects: For such a person may much as he knows, but no more; and that not in this have some particular knowledge and experience of the nature of such a person or such a fountain, that as to other things, knows no more than what everybody does, and yet, to keep a clutter with this little pittance of his, will undertake to write the whole body of physicks: a vice from whence great inconveniences derive their original." Montaigne's Essays.

LIGHTNING AND LIGHTNING
CONDUCTORS.

The mode of the terminal growth of the root [14843.]-ICANNOT agree with " J. T. M." (14814) of plants is a point that has been a good deal either that the motion of a flash of lightning is not controverted. In a thesis on the subject lately perceptible to the eye, or that every flash will have published by M. Flahault, all the various types a visible ascending and descending portion. I think described by different authors are reduced to he can hardly argue from what is observed at the two modes of structure and development-the terminals of a wire circuit during the quiet passage one for dicotyledons, the other for monocoty- of the galvanic current to the state of things at the ledons. It is especially in the mode of forma- moment of the eruptive discharge of lighting. In tion of the root-cap, or organ, protecting the a perfect conductor the passage would no doubt be extremity of the root as it elongates, that the practically instantaneous; but as air is by no means a two types differ. In dicotyledons, this root lightning flash should be progressive, as the expegood conductor, it is not surprising that an ordinary cap renews its cells by successive divisions of rience of ninety-nine persons in every hundred tells the layers of the epidermis. In the mono- them that it is. cotyledons, it is by the internal layer that it is renewed; it is in relation with the epidermis only at the beginning. Another interesting result of M. Flahault's work relates to the very definition of the root. It has been sought

to characterise the root in an absolute manner by the presence of the protective cap, and by its endogenous growth-that is, within the tissues. M. Flahault has shown that there are roots without the cap, and that the principal roots are, in general, not really endogenous.

A downward and an upward lightning flash take place under different circumstances. The up-stroke, or back-stroke, as it is sometimes called, is simply the restoration of equilibrium at one end of a body of charged cloud travelling near the earth at the same instant that a down-stroke has occurred at the opposite end.

The result of my own experience on this point is that, when an electric discharge from the clouds strikes an oak tree, for instance, a considerable portion of the charge is dissipated in air, and it harks and splinters one, or, at most, two branches, then proceeds downwards under the bark of the An American paper gives some particulars stem, dividing sometimes into two or more streams, about the history of water-closets. Their cutting grooves an inch or two deep in the timber, origin is probably Asiatic. The chamber in and then going to earth, and that is the extent of the Palace of Eglon, King of the Moabites the injury. But the discharge of the up-stroke is (Judg. iii., 20, 25) was probably one. They very different, of much rarer occurrence, and far were introduced into Rome under the Republic. from the earth into the tree, and the stem or bole is more destructive. The whole charge passes at once They existed in the palaces of the Caesars, paved completely shattered, every particle of sap being with marble, and ornamented with arabesque converted into steam. On reaching the junction of and mosaics. A water-closet pipe and basin the branches more resistance still is encountered, were recently discovered behind the theatre of and every branch is flung down or left hanging by Pompeii. It was in a water-closet Heliogabalus the bark, most of them being shattered into mere had taken refuge, when he was discovered by splinters as the charge is dissipated into the his soldiers and killed. Water-closets have atmosphere. Such instances are rather rare. I had long been in use in the East, as travellers have the good fortune to witness one about seventeen testified. Tavernier found them in large num-years ago, and photographed the remains of the tree, bers round mosques and temples. They were in this neighbourhood (Hereford) on the night of the and one has just occurred, similar in all respects, first introduced into England in the reign of 7th instant. Elizabeth. According to M. Roubs, they were known in France long previously. Those represented in M. Roub's work (on arts and manufactures) are after the old model with traps, the principle of which is similar to that employed by the early chemists for luting the

water in their alembics.

=

Experiments were recently made by MM. Schwartz and Co., of Berlin (driving-belt manufacturers), on the resistance of leather to rupture by tension. The tabulated results show that no general connection between the strength and the thickness of leather were discovered, and only that the maximum values of the rupturing forces-K (in kilogrammes) for different thicknesses of length, and reduced to 1mm. breadth, are given by the formula K 5:48, while, on the other hand, the minimum values of these forces, independently of the thickness of leather reduced to imm. breadth, appear to be constant, K being about equal to 12k. There is no special use, therefore, in estimating the strength of driving belts in regarding the thickness, as it is much more important to know the probable minimum value of the strength. The average value of the rupturing forces for 1mm. width was K = 205k, with a mean thickness of 5.225mm.; consequently, the limiting value for 1sq. mm. section of leather 25.5k: 5.225 3.92k.

=

As some questions have been asked lately about lightning conductors, I may say that my own plan bas invariably been to use 4in. strips of galvanised iron plate, riveted together, as being the safest and the cheapest. Much of the copper-wire rope I have seen used for conductors is too small to carry a heavy discharge of lightning. I have heard on several occasions of such conductors being fused, as, for instance, one at Stonyburst College a few years ago. The iron band is easily fixed, can be diverted from the straight line at any angle, and if properly terminated above and below, such a conductor will carry off the heaviest discharge in perfect safety. Moreover, it improves as a conductor with every discharge that passes through it, whereas I believe that copper wire becomes more and more brittle.

H. C. Key.

ASCENDING LIGHTNING.

tance, either as a distinct flash or as a diffused dis-
charge or current. It is quite possible, however,
the flash proceeds in both directions at once, and
originates at the two ends, or in the middle, or at
several parts of its circuit at the same instant, all
of these being perfectly consistent with what is
known of electricity. The one explanation which is
(14738, p. 601), and accepted by "F. R. A. S."
not so consistent is that suggested by "J. T. M."
that the apparent phenomens are due to an effect
(14757, p. 627) and "Accinctus" (14780, p. 651),
of persistence of vision, and that the spark appears
to issue from the point at which the observer is
looking. This latter may, as I have just indicated,
be actually the case, and yet the deduction drawn
must be erroneous. What, in truth, has persistence
the total period of the flash? But this flash in its
of vision to do with the matter, except to prolong
entirety is made up of a succession of impressions on
different parts of the optic nerve; persistence of
vision prolongs the apparent duration of each indi-
vidual impression, but cannot affect the order in
which the succession of these impulses is given, and
travels to the receiving apparatus of the brain. If,
then, that receiving apparatus is influenced by so
instantaneous a cause, why should we dispute its
capacity to note the order of its successive actions?
But it is a fact palpable to us all that we do actually
recognise this direction, for the zigzag form of the
spark is itself an evidence of the fact, because it is
nothing but the actual perception of the path fol-
lowed by the spark from point to point of its cir-
of "Accinctus," but it does not seem necessary,
cuit. There may be something in the suggestion
and if the fact were so it would seem to follow that
all our perceptions would be distorted, and that the
optic nerve is a receiving plate not in true focus
with its lenses. As to the question of "A. P.,"
than the other. The result would depend upon
p. 651, there is no more reason to look for one effect
which surface had the positive charge, and also upon
the form of the two surfaces of earth and cloud, and
the earth acting as a point of concentration.
the possible presence of a spring or metallic vein in

Sigma.

DETACHMENT OF PLANETS FROM THE

SUN-PATH OF LIGHTNING. that it seems highly probable that after reaching the [14845.]-IN letter 14778 Mr. D. Kirkwood says point at which gravity was counterbalanced by the centrifugal force ari-ing from the rotation of the contracting spheroid a continuous succession of narrow rings would be thrown off," and no doubt it is true that either rings or fragments of some sort would be thrown off when the point above spoken of was reached. The only question is, has it in fact as yet been reached? The following considerations will show conclusively that it has not. For, if there ever traction of the sun, the centrifugal force" had be had been a time when, by virtue of the continued concome greater than the force of gravity, the same cause still in operation would produce a continual increase; whereas we find that, in all bodies whatever, the force of gravity is much greater than the "centrifugal force." Or, again, in the case of the earth, how can it happen that, with the same cause in operation which once increased the centrifugal force till it became equal to the force of gravity at the equator, it is now only a 289th part of it? In fact, if the equality with the force of gravity at the equator, it centrifugal force has ever been once raised to an of the process which raised it to equality. cannot ever again become less, except by a reversal

PATH OF LIGHTNING.-It is, I believe, generally admitted that lightning very often passes, not from a cloud to the earth, or vice versa, but from one cloud to another. If so must not the cloud to which it passes be negatively charged with respect to the other? And if a cloud can be charged negatively with respect to another cloud, why may it not be so with respect to the earth ?-or, in other words, may not the lightning sometimes shoot upwards

W. G. P.

JUPITER-VULCAN. [14846.]-IN my recent letter (14766), lise 15, there is an error-7h. 45m. being given instead of 8h. 25m. The woodcuts in the next column are a mass of blunders. I entirely fail to identify them as copied from my note-book, except, perhaps, in the [14844.]-THERE seems to be a good deal of inte- cases of Figs. 1 and 4. In fact, Figs. 2 and 5 manage not even to show the positions of the spots at all. rest taken in this rather insignificant matter, and It has been kindly pointed out to me by one of a good deal of confusion of thought into the bar- 66 gain. It is quite certain that if lightning has any spot, and that those spots shown neither of them ours that all the figures do not show the same motion of translation at all, and is not, in fact, omnipresent in its track, it must often ascend. If agree with "F. R. A. S.'s" spot, which careful examination abundantly proves. The longitude of the electric action is single, and passes as a current the spots shown on Fig. 1 are 20° and (a) 88°; or "bolt" from the positive charged surface to the near the centre, Fig. 2, 260°; Fig. 3, 336+; Fig. negative, it must travel both ways, because it is 4, 260°; and Fig. 5, 172° ±. The longitude of well known that the clouds have negative as well as "F.B.A S.'s" spot is 140°, and those of the spots positive charges. Indeed, it is probable that both vi-ible discharge may, therefore, happen in either always co-ex st, and form a complete circuit; the on Mr. Franks' figure, counting from left to right, *The mistake of the figures is Mr. Dennett's own, and the path, and be accompanied with what is called the engravings are as exact reproductions as possible of his return stroke " by some, at perhaps a great dis-sketches.-ED.