to them in usual way (only that Rollers are of tion is poured upon glass in a thin layer, and the THE CHEMICAL COMPOSITION OF course shortened, thus giving another economisa- film so obtained when solidified is well washed tion. This course will involve some alterations in cold water; the non-gelatinising part of the be mentioned. First, the Middle-rails, instead in Building-frame, certain of which must now of dropping 2 inches below under-edge of ManualCheck, must be so set that their under-edge is only one half inch below that point; so just giving hold for the Slip on which Key-frame runs; the Back-rail will of course be carried up with them (see 44, k to p.) Second, there may be now a distinct Front-rail for the purpose of carrying the fore-ends of the Middle-rail. This Rail will be as regards plan so placed that its outer face is flush with fore-edge of front Sidestyles; as regards level it will be so set that its upper edge is low enough to give proper access to the Regulation or attachment of Trackers to Backfall front ends; and note upper edge of Rail had better be exactly where it would if Backfalls came out over Board, then Backfallnose need not be kept clear of inner face of Rail. k.k. The Link-post for foregoing arrangement -now only in. square (or if Rail be of thickness)-will be here tenoned into top edge of this Rail. The thickness of the latter may be if room be very scarce, if not ; its width not less than one-twelfth of its length between Styles. It will be screwed to outer face of Front Spines, but blocked if necessary, for the point of Spine must not be interfered with (as Rollerboard is better attached directly to that): when Arms pass through board very little blocking will be required.

SEA-WATER. the film of jelly, and when this has been done at different depths shows variations, it has been compound soluble in cold water washes out of Norder to decide the question, whether the composition of sea-water in different seas and the film is liquefied and evaporated to dryness, necessary to resort partly to the analyses as before, to ascertain the percentage of solid matter which it also contains after it has been (variously carried out) by different chemists, exhausted of its non-gelatinising part by water. Partly in the examination of specimens of water, The solid matter found will be less than in the procured by different hands, and kept with very unequal care. Hence the inferences drawn have former case, and the difference of the two not been characterised by great exactness. In weights is that of the non-gelatinising matter connection with the German expedition of the present in the original sample. Knowing now Gazelle in 1874-76, an opportunity occurred to the relative proportion of gelatinous matter Herr Jacobsen to examine forty-six samples soluble in cold water to that of the non-soluble of sea-water obtained on that voyage, and carematter or real gelatine, as it may be called, fully kept. He has used them exclusively for sugar is added to a known weight of the concentrated solution in such quantity that the soluble determining the proportions of some of the principal constituents of sea-water taken from the portion, plus the sugar, may be one-half by most various regions and depths. By carefullyweight of the insoluble or real gelatine. A tested and approved methods he has determined definite mixture is thus obtained, which the the proportions of chlorine, of sulphuric acid, patentees use as the medium for the preparation and of carbonate of lime in those samples. of the pigment compound. That the method of operating may be more easily understood, they give an example as found in practice. Suppose the concentrated solution yields on simple evathat the evaporation of 100 parts by weight of poration 20 per cent. of solid matter, and that the evaporation of 100 parts of solidified gelatine, after well washing, yields only 18 parts, the composition of the original bulk or mass is there

(To be continued.)

PIGMENT COMPOUND FOR CARBON
TISSUE.

THE
HE carbon process of photographic printing

fore

Real gelatine insoluble in cold water
Matters soluble in cold water
Water

Parts.
18

80

100

The patentees add to every 100 parts of such a size 7 parts of sugar so as to make the soluble matter one-half of the insoluble, when its composition will beParts. 18

Real gelatine
Soluble Matter
Sugar.
Water.

=

9

80

107

The chlorine was determined in fifteen samples, and showed but small variations. The proportion of the salt-contents to the quantity of chlorine was, at the maximum, 1-8140, at the minimum, 18047, and on an average, 1.80936. Considering that these results are affected by the unavoidable

errors of chlorine-determination and salt-deter

mination, no importance is attached to the irregular divergences met with, and it is concluded that the relative proportion of chlorine in seawater presents no considerable variations.

The sulphuric acid was determined in forty-six samples. It was found to be, on an average, 6:493 per cent. of the entire quantity of salts; the greatest difference, 0.35 per cent. lay between a minimum of 6.34 per cent. and a maximum of 6.39 per cent. Here, too, Herr Jacobsen considers the variations would be diminished if the unavoidable errors, especially of aerometric salt-determination could be eliminated. "Compared, however, with the chlorine-determinations reduced to the same quantities of salt, the sulphuric acid determinations leave hardly a doubt that the proportion of sulphuric acid and of seawater salt is somewhat less constant than its proportion of chlorine. On the other hand, it must be pointed out that no regular connection of the quantity of sulphuric acid with the locality or the depths from which the water samples were taken, was recognisable. The constant motion and mixture of sea-water prevents the local diminution of sulphuric acid from being analytically ascertained with certainty."

The determinations of carbonate of lime were carried out on thirty-nine samples. They gave as result that 10,000 parts of sea-water contain, on an average, 0.269 part of carbonate of lime; the minimum was 0.220 part, and the maximum 0.312 part in 10,000 parts sea-water.

patented improvements, and it promises still to be the fruitful mother of invention. Messrs. O. Sarony, of Scarborough, and J. R. Johnson, of Red Lion-square, have recently obtained the seal for their improvements in the manufacture of pigment compound, by means of which the preparation of "carbon" tissue is facilitated. According to the experience of the patentees, It is well known that glue or gelatine dissolves these relative proportions of soluble matters to in hot water, and that the solution becomes set insoluble gelatine are best for pigment compound or chilled in the form of jelly as the temperature to be used for paper or tissue for the double descends, the point at which the solution sets or transfer process. When the compound is regelatinises varying with the strength or quality quired for single transfer paper, and when workof the gelatine. The higher the temperature of ing in a hot and dry atmosphere, more sugar gelatinisation the better the gelatine. It is also may be required; but as sugar can be easily well known that the jelly loses this quality if the added to the compound and not withdrawn solution be heated for a long period, and loses therefrom, they prefer the proportions given. it more rapidly by alternate heating and cooling, Having thus obtained a standard jelly, they add the temperature at which the jelly resets be- to such a portion of it as represents or contains coming lower after each remelting of the jelly, a 25 pounds of real gelatine, one pound of Indian soluble non-gelatinising compound being formed ink softened and diffused through at least one in the process. Gelatine is used for the prepara- gallon of water, in order to obtain an intense tion of pigment paper or "tissue," as it has black pigment compound. To another like porbeen called, for the purpose of photographic tion of standard jelly" one pound of Indian printing by the carbon process. For this pur- ink and two pounds of alizarine lake are added. pose the gelatine is redissolved and mixed with This must be ground with slab and muller, or in sugar, and the mixture is then heated, churned, a suitable mill, to an extremely fine state of and mixed with various pigments. The ope- division, using very thin solution of gelatine as ration of preparing this paper is one of extreme the medium or vehicle for the grinding process. uncertainty, it being difficult to obtain two A purple tint closely imitating that produced by samples of pigment paper of the same quality photographic printing by the ordinary silver 'Still," he proceeds, "the results are very unless made simultaneously, the nature of the process, is thus obtained. The patentees point much in agreement as compared with previous gelatine varying with the longer or shorter dura-out that there may be considerable variations in data. They justify, in my opinion, a very tion of the heating, cooling, and stirring, or the proportions of colour to gelatine. One-half simple conclusion, though one which is little churning purposes. or even one-third of the quantities given will favourable to some interesting biological and According to the present invention this uncer-yield a pigment compound which will give pic-geological speculations-the conclusion, viz., that tainty is avoided, and a pigment compound is tures. The proportions of pigment given are obtained of definite composition, by adding the indeed somewhat extreme, and will only be found sugar and colouring matter to the gelatine while suitable for certain classes of subjects; but as it is in the state of its first solution after being obtained from the skins, bones, or other raw material, stirring well to incorporate the whole, and after the colouring matter has been well stirred into the solution, pouring it upon plates or slabs, and drying it in thin pieces in the ordinary way. When these are cut up into extremely thin strips they have only to be dissolved by the photographer and employed in the manufacture of tissue in the usual way.

Having obtained a concentrated solution of gelatine direct from the pan of the maker, and before the same has been "slabbed " and dried, the patentees evaporate to dryness in a waterbath a known quantity of the same, in order to ascertain the percentage of solid gelatine contained in the concentrated solution, which is duly noted. Another weighed or measured por

density of pigment can be easily diminished by
the addition of a standard jelly gelatine and
sugar, but cannot be increased, they prefer to
make their compound as stated. A great variety
of colours may be produced by using the various
pigments of the artists, which, however, must be
such as have no action upon the gelatinous
medium. Whatever colours are employed they
must be brought to a state of extreme division by
grinding such as are insoluble upon a slab or in
suitable mills, using weak size as the medium or
vehicle; they are carefully diffused through the
mass of "standard jelly" still in the liquid state,
adding at the same time one-thousandth part of
carbolic acid, then stirring until a perfectly
homogeneous mass has been obtained. The
coloured compound is then "slabbed," dried,
and cut up exactly as ordinary gelatine.

Far from connecting such differences with different localities, or trying to explain them from the conditions of their occurrence, Herr Jacobsen believes they must throughout be attributed to experimental errors which must be the more considerable in such determinations because he was compelled to work with less quantities of water (somewhat less than one litre) than is desirable for the most accurate determinations possible.

66

even the proportion of carbonate of lime in seawater undergoes little variation.

"The influence of abundant secretion of carbonate of lime by organisms, and the also abundant and locally different supply of that carbonate, to sea-water, is quickly equalised by oceanic currents, and, as regards analytical recognition, obliterated. One region of the ocean does not, through containing more carbonate of lime, offer better life-conditions for shell-fish than another, and among the causes from which the most lime-secreting marine animals occur on the coasts, and at comparatively low depths, is certainly not that supposed by J. Davy that, in the open sea, carbonate of lime entirely disappears. Similarly, we are nowise compelled to the improbable supposition of Forchhammer, that shell-forming marine animals must be in a position to transform the sulphate of lime of seawater into carbonate.

In general, researches indicate a very homo

"To the same conclusion led the investigation of the sea-water gases, and, with like necessity, it appears, from the enormous accumulation of constituents that are merely in traces in seawater by many organisms adhering to the sea bottom; it is a conclusion which we everywhere derive from the chemistry of sea-water."

MATHEMATICAL INSTRUMENTS.

VII.*

BY W. MATTIEU WILLIAMS.

the last lecture, some of the instruments for lines were

geneous mixing of the sea-water salt, and this sending instrument, are reproduced by those carried by the frame and passing between the pins again requires, as its ground of explanation, a of the diaphragm of the receiving instru- carried by the magnet. rapid mixture of the sea-water of different ment. A convenient form of free reed alarm regions, a rapid motion of it from place to place, instrument consists of a tube divided by a i.e., general currents in horizontal and vertical longitudinal partition into two chambers, the one directions. of which has at its end an opening to which the mouth is applied, and the other has an open end which is directed towards the diaphragm of the telephone. The partition has through it a slit in which the reed is fitted. In order to increase the noise made by the alarm it is of advantage to provide in the end of the alarm tube a loose hammer or ball which is free to vibrate. This hammer touching the diaphragm, is put in vibration by sounding the alarm so as to give a series of blows to the sending diaphragm, which are reproduced by the receiving diaphragm. Figs. 1 and 2 show longitudinal sections at right angles to each other of a telephone having one arrangement of the invention applied thereto. The iron diaphragm is covered in at top by means of a casing, having a central hole through which, when speaking, the vibrations are transmitted to or from the diaphragm, but which at other times has fitted into it an alarm or whistle. This may be of any known construction for producing a sound by a passage through it of pulses of air.

SIEMENS'S IMPROVEMENTS IN

TELEPHONES.

Amamy to what is known as the relati
N improvement in telephones, relating
has been patented recently in this country on
behalf of Dr. Werner Siemens, of Berlin, the
inventor. The subject of the patent consists of
a modification of the instrument known as Bell's
telephone, and the application to it of a sounding
instrument, so as to produce an alarm calling a
listener's attention to the message about to be

the best of these are liable to considerable error. One of the chief sources of error in ordinary land measurement is the irregularity of the ground The chain or tape must either lie upon the ground and follow its ups and downs, or it must be stretched across the hollows. This stretching, however, does not rectify the curves, for however severely a chan drawn straight. Its own gravitation always bendr or cord, or tape may be stretched, it cannot le it downwards between the points of suspension, and causes it to describe a peculiar curve, to which the name of "catenary," or "chain curve," h been given.

As we cannot stretch a chain straight across valley, over a river, or from peak to peak of mow tains, how are we to measure the length of straigh: lines in such positions?

This problem is solved by the fact that natze provides a practical infinity of such straight lines stretching in every unobstructed direction. These are the rays of light which are continuously thrown off from every visible object. If we can devise s means of measuring them, they are incomparat better than any sort of chain, or bar, or tape other such mechanical measure. Not only do they supply us with straight lines when unobstructed, but we get these lines drawn directly from the ob jects to our eyes, even when the objects are othe wise inaccessible.

The problem then is, first, how to catch thes rays, and then, having caught them, how to ma sure them.

First, as regards catching the rays. Here, a the previous cases, we have to consider our own lations to the external world, or the conditions of sensation. We see objects by virtue of the actre of these rays of light upon our optical apparata (including our external eyes and inner cerebra organs of vision).

The visual position, or apparent direction of object, is determined by the direction in which the rays of light proceeding from that object enter eyes. If the rays comes to us perpendicularly, object appears overhead, if horizontally, it appe on our own level. We refer our sensations o wards according to the direction in which we re ceive them.

If rays of light were to proceed from A (Fig.
FIG.3

B

sent. For this purpose the iron diaphragm of | As shown in the drawing, it consists of a casing
the telephone, which is advantageously made of with an opening at top, and an internal partition
considerable size, is mostly covered by a wood with slit containing a reed, so that on blowing
or other casing having an aperture in the middle through the whole a sharp sound is produced,
for transmission of the sound pulses to or from which by means of the diaphragm is transmitted
the diaphragm, a small space being left between to an ordinary receiving telephone at the other
the diaphragm and its cover sufficient to allow end of the circuit. In addition, the alarm has a
for the vibrations of the former. At the edge of small ball, d, with a stem sliding freely through a
this space holes are made extending out to the guide, so that the ball rests upon the diaphragm
exterior of the casing, so as to allow passage for and is thus caused by its vibration to produce a
pulses of air produced by the sounding of the sharp rattling noise, which is also transmitted to
alarm instrument. The instrument may be con- the receiving telephone. Small lateral channels, E,
structed as a whistle or mouthpiece containing a are formed in the casing through which the air
free or beating reed, which, when not in use, is pulses blown in through the alarm escape into
attached to the telephone by a cord or chain. the open air.
When it is to be used its one end is inserted into
the aperture of the diaphragm cover, which it
fits, and the mouth is applied to the other end,
so as to produce the sound, the pulses of which
causing vibrations of the diaphragm of the

The telephone is by preference constructed of a horse-shoe magnet, with thin polar extensions, G, carrying the coils connected to the circuit, the distance of the poles from the diaphragm being adjustable by means of an eccentric pin

A

to the eye in the direction of the curved line
should not see it in its true position at A, t
would appear to us to be situated at B. If
proceeding from C were to be reflected by a mi
and thence received by the eye, we should see the
object at D behind the mirror.
Rays of light are thus bent and reflected whe
they encounter obstructions, such as
shall presently see, the reflection may betrof
transparent media or reflecting surfaces
account to assist our measurement, but teba
or refraction introduces an element of
manding correction. This is especially the
astronomical measurements.

In ordinary terrestrial experience we f
usually deceived, but see objects in thei
tion by virtue of the rectilinear path of ther
It is by means of this position that we ar
the length of the rays or the distance of the chyard.

from our eyes.

Let us suppose an object situated at

Being a course of Cantor Lecturen Skysuč the Society of Arts.

axis is vertical, provided the permanent adjust-
ments presently to be described have been made.
The middle of the plate is occupied by a compass
with divided ring, whereby the bearings of any
object to the magnetic meridian may be found.
The arrangements for measuring vertical angles
are all above the plate. K and L (Fig. 7) are the
"uprights" which support the horizontal axis of
the semi-circle or vertical limb, M. This semi-circle
is surmounted by an oblong flat piece of brass, the
"stage," to the end of which are screwed the two
Y's, fg, in which the bell-metal collars of the
telescope rest, and are held in their places by the
clips, ii, that are hinged on one side, and held
down on the other by the pins, jj, in order that the
telescope may be readily moved and replaced.

Under the telescope is a long spirit level, carefully constructed, by means of which the horizontality of the telescope is obtained, in order to determine the starting points for measuring its inclination from the horizon when moved upon the

horizontal axis.

telescope, but the inner optical axis that has to be
levelled. The level can only do this work when
itself is parallel with that optical axis. This
parallelism is attained by a special adjustment thus.
Place the telescope roughly level by hand, then
clamp the semicircle by turing the milled head, O;
open the Y clips, ii, and then, by means of the
tangent screw of the semicircle, bring the air bubble
of the level to the centre of the tube; now lift the
telescope from the Y's and reverse it, i.e., place the
collars in opposite Y's, taking care not to disturb the
position of the semicircle. If the bubble remains
in the centre of the tube, it must be parallel to the
axis of the collars (which are of equal diameter),
and being parallel to this, it is also parallel to the
coincident optical axis; if not, the nuts at f, which
raise and lower the level tube relatively to the tele-
scope, must be turned till half the error is corrected,
then correct the other half by the tangent screw P, of
the semicircle. This must be repeated by again and
again reversing, &c., until the adjustment is perfect.
The level should also be adjusted laterally, that it
may be in the same vertical plane from end to end
with the optical axis, as well as parallel below it.
This adjustment is effected by means of the side
screw of the "bubble-cock," and is tested by turn-
ing the telescope with the level a little on either side,
to see whether the bubble travels in such positions.
If this adjustment disturbs that of parallelism, the
latter must be repeated. This being done, the
bubble affords a horizontal zero from which any
inclination of the telescope, upwards or downwards,
may be measured.

call the Welsh or Iberian people. It was not until 607 the invaders took Chester. His object was to speak of this earlier people turned out by the English. He wished first to mention that the Roman invasion had no more influence, so far na blood was concerned, than has British rule in Indis at the present time on blood there. The history of our island begins with the age of steel and ironwith that civilisation of which the term "iron age" is accepted as typical. He had to deal with the pre-historic people. Before the iron age there was what is known as the "bronze age of civilisstion, and further back again than that the "polished stone" age. It was this " "polished stone" age of which he had to speak. The habitations of the people of this age are now known to us from the examination of such traces of groups of dwellings as are met with at Cisbury. The people lived in huts which had roofs to them. Their animals, most probably domesticated, were sheep, goat, or hog, and horse, and there is evidence from the bones that the horse was used for food. The fact One side of the semicircle has an inlaid arc of fact that the horse has ceased to be animal for food silver, which is divided to degrees and fractions, is due to the "ecclesiastical" superstition that, as and is read by the vernier e, which strides over the it was used sacrificially, it was not to be eaten. compass-box. N is the magnifier for this reading. It came to be not the "correct thing" to eat horse. On the opposite side to this magnifier is a clamp, The 'dog, too, was used for food, as well as for grasping a portion of the axis between its bearing herding and other purposes. In all the sites of old on the upright and its attachment to the semicircle. dwellings broken and cut bones of dogs are met The milled head of the clamp screw is shown at O. with. All the bones show they were large dogs, This clamp has a tail reaching down to P, to which not diminutive pets. Still more can be learnt of one ball of a tangent screw is attached, while the the people from their implements. They had potother works in the side of the upright. In directing tery made by hand, not turned on a wheel. They the telescope upwards or downwards, this clamp is We have yet to adjust the verticality of the struck lights from iron pyrites, not from steel, first loosened until the object is sighted, then the vertical axis; or the horizontality of the plate and steel was not invented. They ground com. The clamp is tightened, and by means of the tangent-limb in relation to the optical axis, and thereby, to needles found point to the tailors' and dressmakers' screw the object is brought to its proper place in the be assured that the bubbles, d and d, do their work art being in a fashion followed. They spun and field of vision. accurately. To do this, set the instrument roughly wove apparently, for some of the implements found level, clamp the axis of the limb by H, leaving the could hardly have been used for other purposes. plate free, and move it till the telescope is over two As now, so then, the ear was adorned, and, per of the parallel plate screws; then bring the bubble haps, nose rings were worn. The people, ton, under the telescope to the middle of its tube by the were warlike, and their spears, bows, battle-ares, tangent screw P; now turn the plate half-round; and stones for slings show that they liked then if the bubble returns to the middle, the limb then as much as "civilised" people do now to and plate are horizontal in that direction; but if try the effect of weapons of destruction. They otherwise, half the difference must be corrected by were evidently not a nomadic people, for their the parallel plate-screws under the telescope, and centres of habitations were well fortified, and half by turning the semicircle by means of the General Lane Fox is of opinion that the work tangent screw, P. Now turn the plate 90 deg., or shows as much engineering skill as any fortification quarter round, backwards and forwards, so that works of our own day. The number of stronglythe telescope may be over the other parallel plate-fortified places seems to indicate many tribes who screws, and set its level by them. Having thus enjoyed warfare. There is evidence from implelevelled the plate and limb by means of the tele- ments found, that these people were miners. With scope level, which, by the previous adjustments, all this they were a religious and a superstitious now represents the horizontality of the optical axis, people. Avebury might be called their Westmin the levels on the plate d and d, are to be adjusted by ster Abbey. It was an imposingly grand temple, the screws at their ends, and thus the plate, the and graves clustered around it as burying-place limb, and the telescope axis will harmonise. are now associated with places of divine worship. The tombs contain such things as the departed might want in his future state, and in and around important tombs have been found relics of funeral feasts or "wakes." That there were family vaults is well established, and family peculiarities can be traced in the skulls. Looking at the sum total of what we know of these people, we find in them many of the rudiments of that culture which we now enjoy. Turning to the evidences as to where this people originally came from, the work of archaeologists on the Continent has shown that this Iberian, or, as he would call it, Welsh, race was widespread over Europe. The small dark Basque of the Western Pyrenees showed many features iden tical with what could be made out of the old people. At fairs in some of the Welsh towns, too, the Iberian element could be traced in some of the people who came to them from out-of-the-war places. St. Asaph was remarkable in this respect In Ireland, too, small dark men are to be seen whe if put side by side with the Basque, could not be dis tinguished as regards type. The English who invaded the old "Welsh " or Iberians of our islands were, on the contrary, tall, fine people, with light hair and blue eyes, as is known from history. Although these old Welsh were driven to the moun tain fastnesses, there can be hardly a doubt that the raven tresses and flashing dark eyes we sometimes come across in modern English people are traceable to them. We, at any rate, can trace that they enjoyed the basis of a civilisation of which ours might be an outcome, except where we can tract other influences.

We now come to the telescope itself, to which all the other devices are subservient. I have already spoken of this as the instrument that catches the ray whose direction we have to measure. Practically, we cannot operate upon a single ray, as through even the smallest pin-hole a countless multitude of rays can and do pour. A vastly greater number, of course, pour through the object glass of the telescope, the function of which is to converge all these rays to a point in the focus of the eye-piece, which is a microscope for the examination of the luminous picture thus obtained. The rays proceeding from the object-glass through the telescope thus form a cone of light, and what we want as the equivalent to our typical or fundamental ray is a line constituting the axis of that cone, or the optical axis of the telescope. If by any means we can get a line from the point of the cone straight through the optical centre of the object-glass, and on without deviation to the object under examination, we obtain the above-stated requirement.

This is effected by the device of "collimation." The collimator of a theodolite telescope is a circular diaphragm or plate of brass, with a hole about half an inch in diameter in its centre. I has a rim on its edge, and in this rim are the collimating screws, the heads of which are shown at m. As this collimator or "stop" is held by these screws, it is evident that by pulling one and pushing the opposite, the stop may be pulled towards one side or other of the tube. Coincident with the diameter of the circular opening of this stop are stretched two spider webs, one vertical, and the other horizontal. Of course they cross at the centre of the opening, but how are we to learn that this is the optical centre required?

It is determined thus. In the first place, the drawer of the eye-piece is so adjusted that the spider-webbs are clearly seen, in what is commonly termed its focus. Then a suitable object is selected (the instrument-maker uses a watch-dial nailed to the wall of an opposite neighbour's house), and the intersection of the spider lines is brought upon some clear well-defined point of the object, and the telescope turned round on its collars in the Y's. If the point of intersection of the webbs describes a circle during this turning, the collimation is defective, and the stop must be pulled by the collimating screws accordingly, until the point of intersection falls into the centre of that circle, so that on turning the telescope round again it only turns upon itself as its own centre.

These adjustments being made, the use of the theodolite is simple enough. 1st. To measure the horizontal angles made by the rays from any object to the base line, A B. Place the instrument over the end of the base line (say the terminal, or "bench mark," B) by means of the plummet supplied with the instrument, and which may be attached to the centre of the table-plate of the staff-head. Now clamp the limb in any position, and turn the telescope to the defining object at the end, A, of the base line, and take the reading on the limb by means of the verniers of the plate. Having recorded this reading, turn the telescope to the object, read again as before, and the difference between these two readings is the angular horizontal distance required. The same for any other two objects.

In making these observations the telescope is, as above explained, to be first roughly directed to the object, while the plate free, then the plate is clamped, and the accurate bisection of the object by the spider lines is obtained by means of the tangent-screw.

Vertical angles of elevation or depression are taken simply by starting from the horizontal position of the telescope, given to it by it its level, then elevating or depressing the telescope to the object, aided by the clamp and tangent screw, P, and reading the semicircle.

(To be continued.)

We thus secure a coincidence of the optical axis of the telescope with the axis of the collars, i.e., the EARLY INHABITANTS OF BRITAIN. line connecting their centres. This line (assuming

the absence of atmospheric refraction) continues

directly from the eye to the object, and thus the optical direction of the telescope coincides with that of the central or typical ray whose direction we require to measure."

As already stated, the level, fg, is used to determine the horizontality of the telescope, but, as now will be understood, it is not the outward and visible

• Another mode of collimating, effecting the same result, is to adjust each web separately. First make the horizontal web cut some definite point of the object, then turn the telescope half round, and if the web now stands above or below, move it half the distance of the error and try again, until it cuts the same point in both positions of the telescope. The vertical web is then treated in like

manner.

T

Atstitution last week Professor Boyd Dawkins

gave an interesting summary of what has been
learnt of the early inhabitants of this country from
pit and cave explorations. Enough, he said, was
now known of them for some of their characteristics
to be traced in the present population. The claims
of race have lately been urged in the cry of Pan-
slavism, and we ourselves take pride in recognising
an Englishman as an Englishman, whether he is
born in Britain, Australia, or America. The history
of the "English" from their invasion of this
country in 449 is fairly well known. It took two
centuries from their first landing at the Isle of
Thanet for them to drive back, district by district,
the inhabitants they found here, whom we should

SOME EFFECTS OF AMALGAMATION.*
MER

ERCURY, although electro-negative to dr in a voltaic combination, has the property in common with palladium, platinum, and nickel, of absorbing hydrogen, and assuming in ca quence, the electro-positive polarity of the metal with which it is associated, provided that the potential be insufficient to disengage the hydrogen in the gaseous form.

mercury, excited by sulphuric acid solution, vil A couple, consisting of amalgamated in generate a current for a time dependent on the extent and nature of the surface of the mercy

* By Mr. F. HIGGINS, in the Telegraphiz Journal,

This current will gradually diminish and cease, only from the assimilation of polarity caused by the absorption of hydrogen by the mercury.

If the mercury be pure and its surface smooth, the polarisation is much more complete than if it be rough, or contain any metal which is not very soluble in it, such as copper. In this latter case, the impurity floats to the surface in a finely divided state, and exposes points which greatly assist the formation and disengagement of bubbles of hydrogen.

Even when this roughness is caused by an excess of zinc, the mercury only very slightly protects the zinc from solution. On the other hand, the presence of lead or tin, which are very soluble and form smooth amalgams, does not appear to prevent the polarisation of the mercury, and does not facilitate the evolution of gas.

The action of an amalgamated zinc plate in a battery is probably, therefore, to a great extent of a secondary nature. The mercury dissolves and exposes zinc to the action of the acid, a voltaic couple is thus formed between the zinc and the mercury in its vicinity; the zinc necessarily oxidised and dissolved on this account is not, however, wasted, as in the case of continuous local action, but by its combustion lays up a store of electropositive gas in the nascent state on the surface of the mercury.

The action resembles in a great measure that

suming reserves previously accumulated, exhausts
itself, and dies. This part of the spectrum, however,
though necessary, is not sufficient. Behind red glass
plants may no doubt live long, but they get excessively
elongated and slender, and their leaves become
narrow and little-coloured. This is owing to the
absence of the blue violet rays. Thus each region
of the spectrum contains parts that play an active
role in the life of plants. Now turn to animals:
M. Yung has experimented during three years on
the effect of different spectral colours on the
development of the eggs of frogs (the common frog
and the edible frog), of trout, and of fresh-water
snails. It was found that violet light favoured the
development very remarkably; blue light comes
next in this respect, and is followed by yellow
light and white light (which two gave nearly
similar effects). On the other hand, red and green
appear to be positively injurious, for it was found
impossible to get complete development of the eggs
in these colours. Darkness does not prevent
development, but, contrary to what some have
affirmed, retards it. Tadpoles of the same size,
and subjected to the same physical conditions
previous to experiment, died more quickly of
inanition when deprived of food in violet and blue
rays than in the others.

READING AND EYESIGHT.

SOLID END CONNECTING RODS.

BY JOSHUA ROSE, M.E.*

N Fig. 1 is shown the simplest form of solidended connecting-rod. It has but one brass, and the adjustment is made by the set-screw shown, to which there is sometimes added a check-nut to prevent the screw from slacking back. During the pulling stroke of the rod the whole of the strain is concentrated on the end area of the set-screw, and this causes it to imbed in the brass, giving play to the brass unless frequent adjustment is made. It is difficult to readily obtain a very accurate adjustment with a simple set-screw of this kind, and furthermore the rod gets, as it were, shorter from centre to centre of the bore of the brasses. Fig 2 is shown a form of end not unfrequently used upon very small rods. The rod-end screws into the brass A, so that when it wears shorter to the amount of half the pitch of the thread upon the rod-end, the brass may be unscrewed half a turn, and the original length will be restored. The cap is held on by two screws, which may have slotted heads as shown, or screws with check nuts to prevent the screws from slackening back, as all screws are apt to do that receive sudden strains in reverse direc

tions.

In

In Fig. 3 is shown a very substantial form of solid-ended rod, a plan view being shown in Fig. 4. The back brass A has a flange, as shown, in Figs. 4 and 5 at A, which secures it to the rod end at the back. The front brass B, Figs. 3, 4, and 6, has the key-way partly sunk in it, and the key binds

which takes place in a secondary battery, except M. the question, Why is reading a specially against one side as well as on the bottom of the

the cell.

The diminution of internal resistance which may be thus effected in batteries is of great consequence: like the friction in a steam-engine, the less there is of it the more power there is available for useful work without increased cost. But the most useful application of this property of amalgamated surfaces is to the protection of the connections of zinc plates from destruction.

An iron wire cast into a zinc plate will outlast the zine; copper, on the contrary, is frequently attacked near the surface of the liquid, and the amalgamation of copper causes a steady destruction of zinc by local action from the before-mentioned property which it possesses of roughening the surface of the mercury in which it is dissolved.

JAVEL, in a recent lecture, tries to answer that the loss in translation is much less in consequence of the absence of an external circuit, the fatiguing exercise? and also suggests some reme-key-way, and this draws that brass close down to whole force of the combination being exerted within dies for this fatigue. First, M. Javel says reading the face of the rod, as shown in Fig. 4. In order found that an amalgamated iron surface, polarised eyesight, resulting in a permanent tension of the while at the other end it is placed inside or between In proof of the foregoing suppositions, it has been requires an absolutely permanent application of to cause the rod to maintain its original length, the key at one end is placed outside the crank-pin, by being placed in contact with a fragment of zinc, organ, which may be measured by the amount of the crank-pin and the stem of the rod, as shown in acts as well as a plate of zinc of the same size, fatigue or by the production of permanent myopy. Figs. 3 and 6. In this, as in many solid-ended and, while affording the same conductive power as Secondly, books are printed in black on a white rods, the flange or collar of the crank-pin requires a large plate, the waste by local action is only pro-ground: the eye is thus in presence of the most to pass through the brass opening of the rod. This portional to the surface of zinc actually employed. absolute contrast which can be imagined. The may be accomplished by making the brass opening third peculiarity lies in the arrangement of the cha- large, or wide enough to pass over the crank-pin This arrangement has some advantages to recom- racters in horizontal lines, over which we run our collar (which will increase the width of the brasses, mend its employment, one of which is that the eyes. If we maintain during reading a perfect im- and hence that of the rod-end); or else the crankpositive plate, or rather connection, can be a fixture mobility of the book and the head, the printed pin collar may have two flat places filed on it, as in in a battery, and may be in the shape of an amal- lines are applied successively to the same parts of the end view shown in Fig. 7. The objection to gamated wrought or cast-iron cup, into which zinc the retina, while the interspaces, more bright, also this plan is that the rod can only be taken on and may be dropped as required. Such a cup would be affect certain regions of the retina, always the off in one position of the engine that is, when the indestructible if kept supplied with zinc. same. There must result from this a fatigue ana- two flat places A and B, Fig. 7, stand parallel with logous to that which we experience when we make the length of the rod. experiments in "accidental images," and physicists It will be noticed in Fig. 4 that the brass B does will admit that there is nothing more disastrous for not fill the space in the rod. This is because that the sight than the prolonged contemplation of these brass has to pass in over crank-pin collar and push images. Lastly, and most important of all in M. up into the journal after it is in the rod. To Javel's estimation, is the continual variation of the make this space as small as possible, and to enable distance of the eye from the point of fixation on giving the crank-pin as large a collar as possible, the book. A simple calculation demonstrates that the key brass (B) is sometimes bevelled off, as shown the accommodation of the eye to the page under- in Fig. 8 at AB. Another form of this rod-end is goes a distinct variation in proportion as the eye shown in Fig. 9. in which there are two keys to the passes from the beginning to the end of each line, brasses, the object being to adjust the keys to and that this variation is all the greater in propor- maintain the rod of its proper length. In order tion to the nearness of the book to the eye and the to facilitate making this adjustment, there should length of the line. As to the rules which M. Javel always be upon the face of the rod-end centre inculcates in order that the injurious effects of punch marks, as shown in Fig. 11 at FG, or else reading may be avoided, with reference to the per- two deep marks, as shown at CD in Fig. 10. mauent application of the eyes, he counsels to avoid Then, in lining up the brasses to set the key back, excess, to take notes in reading, to stop in order to the rod may be restored to its original length by reflect or even to roll a cigarette; but not to go on putting behind the back brass a piece of metal of reading for hours on end without stopping. As to the such thickness as will bring the centre of the bore contrast between the white of the paper and the black of the back-brass B even with the centre-punch of the characters, various experiments have been or other marks. This being the case, it does not made in the introduction of coloured papers. M. matter about the exact thickness of the piece of Javel advises the adoption of a slightly yellow tint. metal put behind the other brass, since a variation But the nature of the yellow to be used is not a in that will only act to let the key come more or matter of indifference; he would desire a yellow less through the rod-end without affecting the resulting from the absence of the blue rays, analo- length of the rod. (This remark does not, howgous to that of paper made from a wood paste, and ever, apply to rods in which there is a strap which which is often mistakenly corrected by the addition moves as the key is set up.) In Fig. 10 is shown a of an ultramarine blue, which produces gray and form of rod-end sometimes used. The end being THE as to life both from practical observation and also theoreti- whole strain of the pull of the rod falls upon the HE question as to how life is affected by tho not white. M. Jayel has been led to this conclusion open, the brasses pass through it. In this case the various times engaged attention, and plant life has cally from the relation which must exist between edge of the gib at top and bottom of the strap, apparently been more studied in this respect than the two eyes and the colours of the spectrum. causing the gib to wear out very fast; furthermore, animal. Two distinct series of researches lately His third advice is to give preference to small the back brass condenses the metal at the back of described to the French Academy seem to afford volumes which can be held in the hand, which ob- the brass opening, acting to pene it and throw some fresh insight into the matter, and it is inter-viates the necessity of the book being kept fixed in one the points of the rod-end open, which it always esting to compare them together.' One series, by place, and the fatigue resulting from accidental does, the jaws of the jib embedding in the jaws M. Bert, was on plants; the other, by M. Yung, on images. Lastly, M. Javel advises the avoidance of of the rod. This opening of the rod-jaws makes the eggs of certain animals. M. Bert kept plants too long lines, and therefore he prefers small the brasses loose in their places; hence this within a glass trough enclosure, containing an al- volumes, and for the same reason those journals is a weak and undesirable form of rod-end, coholic solution of chlorophyll (very frequently which are printed in narrow columns. Of course though very convenient to take on and off. renewed) and exposed them thus in a good diffuse every one knows that it is exceedingly injurious to In Figs. 11, 12, 13, and 14 are shown a form of light. The solution, which was very weak, and in read with insufficient light, or to use too small solid-ended rod of more modern construction. a very thin layer, intercepted little more than the print, and other common rules. M. Javel concludes In this case a wedge (A) is used instead of a characteristic region of the red in the spectrum. by protesting against an invidious assertion which key being adjusted by screws passing through This excluded part, then, was proved to be the has recently been made "in a neighbouring the rod at the top and bottom, it being obvious indispensable part of white light, for the plants country," according to which the degree of civilisa- that the set-screws may have check-nuts added. B immediately ceased to grow, and before long died. tion of a people is proportional to the number of is the back brass, and Ĉ the key brass. In this case It is in this red region (as M. Timirigzeff has lately the short-sighted shown to exist by statistics; the the flange of the brass goes next to the crank-pin, shown) that the greatest reduction of carbonic acid extreme economy of light, the abuse of reading to and a plate, D, is provided to serve as a flange on takes place. If red rays are kept from the leaf the plant the detriment of reflection and the observation of the front face of the brass. In fig. 11 this plate is can no longer increase its weight, it is reduced to con- real facts, the employment of Gothic characters removed to show the wedge, A; but it is shown in and of a too broad column for books and journals the Plan View 12 and the End View 13, and by are the conditions which, M. Javel believes, lead to itself in Fig. 14. A groove is cut on each side of myopy, especially if successive generations have been subjected to these injurious influences.

If it were possible to amalgamate the armour of submarine cables it might perhaps increase their durability. Or the inner sheathing employed to resist the attacks of the teredo might be of a thin ribbon of amalgated galvanised iron, which would have the great advantage over copper of not hastening or assisting the decay of the iron wires, when as would most likely be the case after the cable had been submerged some time, the two sheathings should come into contact.

LIGHT AND LIFE.

This is only correct within certain limits. The zinc exerts its influence promptly over a radius of two inches, but more slowly as the surface is enlarged.

In the Scientific News.