pump, but hopeless in the case of a dynamo. correct. If we lengthen the pipes or make Col. Smith states that he is providing his with them of smaller diameter, or roughen the ina tail, and he will therefore get its maximum sides, not so much water will flow in the same [130.-IS SPACE INFINITE-The ques-The question then arises: Why is this type of wire, making it thinner, or making it of some efficiency, and constant direction of rotation. time as at first analogous to lengthening a tion "Is Space Infinite?" (130, p. 114) was mill not usually made? I suggest that Col. material which is not so good a conductor, and under discussion before the commencement of Smith will find the Pantanemone too slow for a thus offering greater resistance to the current, the Christian era. Lucretius (1 B.C.) considered dynamo, nor will it drive with light winds if which will become less thereby. If a primary that " the atoms of which the universe is com- geared up. T. M. Hartley. cell shows a potential difference across its terBosed would long ere now have been unitod minals of 1 volt while passing a current of [144.]-STEAM ΤΟ AMERICA. The 5 amps., then inserting a lamp into the circuit in the centre of the system if it had not been Museum of Science and Art," edited by Dr. will reduce the current, since the lamp offers so infinite as to have no centre." Sir Isaac Lardner, Vol. X., p. 119, contains a full resistance to its flow, but may have the effect Newton, in reply to Dr. Bentley, December 10, account of his case with respect to steam. navi- of very slightly raising the P.D. at the ter 1692, wrote: "If matter were evenly diffused gation across the Atlantic. As that work may minals. A better aspect of the case would be through finito space and endowed with innate of the statement may be serviceable. It ap a resistance of such an amount that a volt. not be accessible to some readers, a summary to suppose a current of 5 amps. to flow through. gravity, it would fall into the middle of the pears that at the British Association meeting, meter joining the ends of the resistance indispace and form one great spherical mass; but 1836, two schemes for steam navigation to cates a pressure of 1 volt. Then, supposing a if it were diffused through an infinite space, America woro discussed-one being for a ling lamp having a resistance of 19.8 ohms he put some of it would collect into ono mass and from the west coast of Ireland to Boston, and in the circuit, the current will be reduced, and some into another, so as to form an infinite the other for a line from Bristol to New York. the voltmeter will show a smaller reading. number of great masses ("Life of Newton, Dr. Lardner supported the Ireland Boston Example: First case, C5 amps, V = 1 volt, Brewster, Chapter XVI., p. 285). Einstein scheme as being the shorter route, and more ascribes the earliest discussion in detail to the feasible from the commercial point of view. R one-fifth of an ohm, this is th astronomer Seeliger, and states that "the first At the B.A, meeting, 1837, Dr. Lardner again answer that suggests itself is that as regards advocated the short route, and to substantiate resistance of the resistance. Second case, total space (and time) the universe is infinite. his statement he quotes from a report of the resistance of lamp and wire 19.80.220 This view is not in harmony with the theory of meeting that appeared in The Times: "He ohms; available voltage 1 volt; therefore, Newton. The latter theory rather requires that was aware that since the question had arisen V 1 the universe, should have a kind of centre in it had boon stated that his own opinion was C one-twentieth of an ampere. which the density is a maximum, and as we averse to it. This statement was totally wrong, prooded outwards from the centre the group but he did feel that great caution should be density of the stars should diminish, until used in the adoption of the means of carrying finally, at great distances, it is surrounded by the project into effect. Almost all depended an infinite region of emptiness. The Stellar on the first attempt, for a failure would much universe ought to be a finite island in an in- rotard the ultimate consummation of the profinite ocean of space ("Relativity," XXX., ject" (The Times, August 27, 1837). Dr. p. 105, by A. Einstein, translated by R. D. Lardner goes on to say: "What I did affirm in Lawson, D.So.). From the foregoing it appears 1836-7 was that the long sea voyages by steam that Einstein was not fully conversant with the which were contemplated could not at that historical aspect of the question nor with New-time be maintained with that regularity and ton's theory respecting it, and, further, that ho overlooked the contingency that there may be an infinite quantity of matter, in which case it could not be collected into a finite island.' A later pronouncement of Einstein was, Is spaco infinite? It is here that my opinion differs from that of Eddington. With Mach, I feel that an affirmative answer is imporative, but for the time nothing can be proved [161.]-VOLTS AND AMPS.-The querist ("Naturo." February 17, 1921). More recently is evidently far from clear upon the difference ho said he was of opinion that the general between volts and amps., or upon the signifitheory of relativity could only solve this cance of Ohm's Law He has no cause, howproblem satisfactorily by regarding the unievor. to be ashamed of himself. Many who verse as spatially finite and closed " ("E.M.," Vol. CXIII, p. 231). Under the impulse to [156.]—POTASH IN TANHOUSE BARK would not readily admit the fact would find give an "affirmative answer to the question Potash from oak brushwood ash averages about difficulty in clearly expressing the relations E of which he said "nothing can be proyed," 8 per cent., and phosphates about 8 per cent. embodied in the simple equation, C Ꭱ . Professor Einstein introduced mythical flat About cwt. ash results from burning one ton boings existing on a spherical surface, of which of wood. W. J. O. F. text-books fail, as a rule, to clearly impress the great circle was upon the student's mind the connection bea self-contained line of dofinite length, which can be measured by [161.]-VOLTS AND AMPS.-In all electween voltage, amperage, and resistance in a means of a measuring rod. Similarly, this rical problems dealing with dynamic elec- circuit. dynamic elec-circuit. A clear understanding of this connecuniverso has a definite area which can be com- tricity-that is, electricity in motion-there are tion is essential. Firstly, let us see how Ohm's pared with the area of a square constructed three fundamental quantitics always presont to. Law is arrived at, and immediately and for with rods. The great charm resulting from gether. First, the quantity of electricity (called evor forget the symbols E.M.F. for voltage. this consideration lies in the recognition of the the current or amperes) flowing along a wire Instead, let us only think of voltage as fact that the universe of these beings is finite, or through the filament of a lamp or through suro difference" oxisting between two points, and yet has no limits" ("Relativity," any apparatus connected with the source of and let us refer to any voltage as a P.D. The XXXI., p. 109). The first answer that suggests supply-e.g., a primary cell. Second, the elec-qucrist will see at once then how amperage itself is that only a limited number of such trical pressure (called the volts, electromotive comes about. Whenever a difference in presthings as, say, postage stamps, could be stuck force, or potential difference) available at the sure exists thero is always a tendency for a on the spherical surface, and, therefore, to source of supply for driving the current through flow to take place from the region of high say that it "has no limits " is not a correct the wires and other apparatus-e.g., the E.M.F. pressure to the region of low pressure. The statement. Some such objection, may have of a primary coll. Third, the amount of ob- same tendency exists in the case of electrical presented itself to Einstein, because when lec- struction (called the resistance) offered by the pressures. Between the terminals of a battery turing last year and using the same object-wires, apparatus, and source of electrical energy in working order there is a P.D. Very well; losson-on which occasion the flat boings were -e.g., the resistance of the whole circuit. The put a nine between them, and a flow takes circular beetles-he said "only certain above three factors are always present in every place. The pipe one uses is a conducting wire. number of beetles of dofinite size could in- circuit through which an electric current flows. If the pipe is very small in bore and prevents habit such a sphere" ("E.M.," June 17, 1921, Now for analogies. Look upon a current of a rapid flow, we say it has a high resistance; p. 270). The burden of carrying conviction electricity-the amperes-flowing along a wire the flow. then, is only a slow one-in other was then transferred to the shadows of the as a curront of water flowing through a pipo; words, the amperage is low. Conversely, the. beotlos! The opening words of "Fragments look upon electrical prossure-the volts-as the flow is rapid if the conductor is of low reof Science," by Tyndall, 1871, are: "We canamount of pressure behind the water flowing sistanoc. not think of spaco as finite, for whenever in in a pipe; look upon electrical resistance the imagination we erect a boundary wo aro comohms--as the resistance offered by the inside pelled to think of space as existing beyond of the pipe to the water flowing through it. that boundary. Thus by the incessant dissolu. Suppose a cistern containing water to be placed tion of limits wo arrive at a more or less adoon the roof of a house and 30 ft. above the quate idea of the infinity of space." That may ground, and let two pipes be fixed to the be taken to represent the view of the average cistern and carried to the ground-one pipe person who thinks of these questions, and in having an inside diameter of 6 in., and the the long run it is the opinion of the average other only 1 in. Both pipes have taps fitted to man that counts. The question is purely specu- their lower ends, also pressure gaugos. While lative, and rather unprofitable speculation, unthe taps are closed, each gauge will show a less it be rogarded as intellectual gymnastics; pressure of 15 lb. per square inch., since the the same may be said of the Einstein theory. pressure of water per square inch is nearly lb. per foot of height. Now open both taps. and note that the pressure, as shown by the gauges, is nothing (this is equivalent to a short-circuit if each pipe leads to a separate tank). It will be found that the tank connected to the 6-in. pipe contains thirty-six times as much water as that connected to the 1-in. pine, because the area of the 6-in. pipe is thirty-six times greater than the 1-in. For water this relation is not strictly correct, but for electricity flowing through wires of the samo metal and conductivity it is absolutely [132.]—PANTANEMONE.—With reference to Col. Smith's reply, there are one or two points which were not cleared up in the original description. The principal claims were that it would work with wind in all but two directions, that a very light wind would drive it, and that it would stand severe galos. It was not mentioned that it would turn in opposite directions according to the direction of wind. This would be no dotrimont when driving a In other words, the amperage is high. So voltage is the difference in pressuro which causes amperage, and resistance is the property of the conductor which says whether this amperage shall be high or low. Before leaving this elementary but vitally important consideration of the electric circuit, let querist learn that the P.D. between the terminals of a battery on open circuit (the terminals not connected together) is by no means the same as that when the terminals are connected by a circuit. circuit. It is always higher in the first case, because so long as any electrical flow is taking place from one terminal to another, the differenco in pressure between the terminals is being equalised. Querist may think these facts over: (i.) If the circuit between the terminals had no resistance, then the P.D. would become zero and the amperage infinitely large (theoretically); (ii.) if the circuit has complete resistance (this is the usual condition, when air or some insulator constitutes the circuit), then the P.D. is at its maximum value, and the amperage is nil; (iii) the amperage at anv part of a circuit is the same as at any other part; (iv.) the voltage or P.D. will be different moa at different lengths of circuit, being greatest if under the arrangement with the Government, I R f I R of the cirouit, whence C = E; C There circuit of resistance R. he will find no difficulty B' [161.-VOLTS AND AMPS.-Evidently "B" is not acquainted with Ohm's Law-i.e., that the strength of the current flowing be tween any two points of a wire is directly pro: portional to the electromotivo force in that wire-or, what is the same thing, the difference of potential between the two points is inversely proportional to the resistance between the two points. If your cell has a pressure of 1 volt and you insert a resistance of 2 ohms in the E. circuit, then, by Ohm's Law, C amp. R Therefore, if you increased your pressure or voltage to 2 volts and the resistance remained constant-i.e., 2 ohms-your current would be 1 amp., and so on. On the other hand, if you increase your resistance to 4 ohms, then by Ohm's Law your current would drop to amp., inversely proportional to your voltage, The best analogy to make this point clear to a beginner is to consider volts as pressure in a steam boiler, resistance as a throttle, and current the quantity of steam regulated by the throttle. The deflection of the needle is due to current more than yoltage, by virtue of the well-known law that, any current-carry ing conductor will have lines of force flowing round it which set themselves at right angles to such conductor having North and South poles so long as the current flows. The differonce in the lamps is that one has a finer or longer filament, which increases the resistance, in other words, applying Ohm's Law, [172.]—BARLOW LENS.-I. have not yet lens. Would some kind reader please explain seen any reference in "Ours" to a "Barlow" what this is?-Dynamotor. now [173.]-PHONOGRAPH RECORDS.-I have for been endeavouring some time to make records at home on an Edison phonograph, and have got fairish results, piano, duets, quartettes, or anything that but find it well-nigh impossible to record violin, necessitates the performers being a little distance from the recording horn. How would a microphone, a very sensitive instrument, and microphone do in this case? I have a Fenwick supposing I got a little receiver made to fit in place of the recorder, and having the cutting David J. Smith.styli attached to the centre of diaphragm, and [166:] ANDROMEDA NEBULA. -The connected with a battery to the microphone, density of this nebula, such that its attraction of would this give a better engraving of the vithe Earth should equal the Sun's attraction, brations on the wax?-Clement J. Williamson, would be about that stated by "H. L. W.," New Street, Scalloway, Shetland. but since the data are not known with any [174.]-CUTTING CIRCULAR HOLE IN accuracy, it is useless to go into detail. More- GLASS.-Would any reader give a satisfaca mass many million times that of the whole of 1 in. to 4 in. diameter in a sheet of glass over such a density would give the nebulatory method of cutting a circular hole from the stars in the galactic system, and hence is not with diamond cutter, or any other satisfacworth consideration. As regards the Orion tory method?-C., E. M. Nebula, I am not aware of any estimate of its mass or density on which even the roughest calculation of gravitative effect could be based; such an' estimate, indeed, appears nearly impossible, in view of the way in which, this nebula extends over at least half of the constellation, with apparently very varying density. K. Q. [169.]-CLEANING WINDOWS.-Hundreds of methods recommended in past volumes. Two of the best, especially for very bad stains, will be found on p: 171 of "Ours" of October 28, 1921, which I have no doubt can still be had from the publisher for 4d., post free. Gyp. be done satisfactorily by allowing the mercury to [170.]-CLEANING MERCURY.-This can cury [175.] FIRELESS COOKER. I am making a cooker, the outside shell being a sanall wooden barrel 12 in. high by 12 in. tin cylinder. What is the best packing to put diameter. Inside this I ann putting between the two for insulation? afford asbestos or slag wool. Will sawdust, well rammed, act? Would it be any advantage to mix alum or water-glass with it?Cook. PLATE. Can any correspondent kindly say [176.]-MULTIPLE IMAGES ON PHOTOwhat is the procedure in order to produce using the cornea of insects for the purpose multiple images on a photograph.c plato thereof?-W. H. C [177.]-LEATHER DRESSING. Required, that is dry and cracking, not a polish for the a dressing for leather covering of furniture woodwork. Must not affect colour or remain sticky. Loather is morocco. H. W. ་་ દી [178.-SCREW COUPLING.-Why is weight formed at the End of the arm or lever used to tighten the screw coupling of railway carriages? Is it to assist the swinging over of the lever above the coupling, or is it for keeping the lever down, and so prevent any [170.]-CLEANING MERCURY.-I can slackening back of the screw when the train sympathise with "Tressler," having experi-is running? Would a coupling have a tenenced the same difficulty in trying to clean mer-dency to slacken only when not properly condensed milk tin. It is quite likely that your not slacken at all, either with or without a which some silly person had stored in a tightened up, and a tightly screwed up one besides being oxidised, in which case a week's mercury contains a small amount of amalgani, weight?-Slacker. filtering will not brighten it. Drastic chemical treatment is necessary. Pour the mercury into LATHE. There is some way of cutting worm. [179.] --CUTTING WORM WHEELS ON A a large flask, cover with a little water, and add wheels on a lathe. They are at present cut trong nitric acid-sufficient to cause the liquid with a "hcb" made specially for each job; to fiz:z. briskly. This is best done outdoors the cost of this is prohibitory. On the lathe on account of the nitric oxide fumes (and over a a profile cutter, the shape and size of thread large basin, in case you break the flask). Keep on worm, is inserted in a boring-bar projectthe mercury moving as much as possible, suping to swing the radius of worm used; the porting the bottom of the flask with one hand boring-bar is between centres. The blank (a minute or two is generally sufficient to cleanse wheel to be cut is first turned hollow on the the metal, and the loss is very small). Then add face to the curve of worm, then laid haria large quantity of water; shake, and decant; zontally on a pivot free to turn at the height repeat until the washing water is perfectly clear. of lathe centres; on the top of blank is laid Pour into a basin, suck up the excess wator a gear-wheel fastened to blank; there is a with blotting paper, and finally filter once or geared connection between this blank twice through pin-pricked filter paper. the change-wheels of lathe, and also with a dividing head. As the cultor ir boxing-bar [171.]---WASTE TINS.-Recovery of tin has sweeps through the face of blank a slight been worked in England, but it is difficult to rotation is given equal to the pitch of thread make it pay, not because of the recovery process tooth by dividing head. Will on worm used. The blank is then turned one. itself, but because of the cost of collection of tooth by dividing head. Will some experisufficient scrap to keep a works going. The reencod reader explain how this is done, and sultant iron scrap is nearly worthless. After the oan it to done on a milling machine? This is old tins have been cleaned by boiling in caustic a very important item in engineering work soda solution, the solder is melted off, and then and is not generally known by the trade. 1 the scrap is made the anode in a hot solution of pays best to get large worms and wheels cass. salt and caustic soda, from which tin deposits in recently required I .{L cut wheel 16 in. asked a spongy form. Many processes have been diametor and was patented since 1885. £40 for it.-Old K. Q. Reader. [180.] SILICO.-I shall be obliged if some correspondent will let me know of what Silico is composed, for what purposes it is used, and, if used in combination, what are the reactions and resultants? I fancy it has something to do with generating gas for balloons.-Keeley. The Vate Mr. J. T. Norman-Thomas, F.L.S., of Blundelsands, who the 2-volt lamp. Their candlo-power, or wattage, doyen of local naturalists at the time of his remains the same-Le.. watts v. × amps. 4 x .5 2 watts. 2 v. x. 1 a. = 2 watts 2 c.p. in cach lamp. A. Platt. death at the end of last year, had amassed a [163.]—HARDSTOFT OIL-Are not thinking of the oil-well of this name in Derby shire? This was the first of the ol-wells bored a |