490 



NATURE 



[June 24. 1909 



The Saiitic-Aslroiiomical and Universal Calculator. 

 The .Miclianical Solving of all Arithmetical 

 Prohlcnis, r.lane and Spherical Trigonometry, in- 

 cludiny Terrestrial and Astronomical Navigation. 

 By R. Nelting. Tp. by. (Hamburg : R. Nelting, 

 1909.) Price 4 marks. 

 In many numerical processes there has been too great 

 a tendency on the part of computers to employ more 

 decimal places than are necessary, and to use logar- 

 ithms where more direct methods would be effective. 

 The introduction of mechanical contrivances for the 

 porformance of arithmetical operations has brought 

 the problem of a possibly greater simplification of cal- 

 culation more to the front, with the result that some 

 neglected resources have been made available. One 

 outcome has been the improvement in accuracy and in- 

 genuity in construction of sliding scales for obtaining 

 an approximate solution of many simple problems. 

 With increased usefulness, however, comes a tendencv 

 to increase the number of moving parts and to give 

 greater variety to the system of dividing, but this 

 more complicated mechanism often destrovs the sim- 

 plicity of construction which is one great merit in 

 the sliding scale. Certainly, the invention described 

 by Mr. Nelting docs not err on the side of simplicitv. 

 The inventor claims for his calculator that it will 

 give the logs, of numbers, with their squares and 

 square roots ; the values of trigonometrical functions 

 of sine, tangent, cosecant and cotangent of angles, 

 whether expressed in time or in arc ; tables of re- 

 ciprocals with their squares and square roots. In 

 addition to many other combinations, the scales can 

 be used for facilitating or completelv solving problems 

 required in nautical astronomy connected with alti- 

 tude, longitude, and latitude, with an accuracy suffi- 

 cient for the pur|X)ses of navigation. Unfortunately, 

 we have not had an opportunity of studying the 

 mechanism, and the rules that arc given for its use 

 are not easily followed when the necessarv construc- 

 tions cannot be made. Moreover, the description is 

 obscure in many parts. 



The Theory of Electric Cables and Networks. By Dr. 

 Alexander Russell. Pp. x + 269. (London : A. Con- 

 stable and Co., Ltd., 1908.) Price 8s. net. 

 We opened this book expecting to find it filled with the 

 solutions of rather unpractical problems, the solutions, 

 however, being of considerable importance in higher 

 mathematics. We find that it is a very practical 

 treatise which will prove useful to the increasingly 

 numerous class of electrical engineers who deal with 

 distributing networks, their insulation and faults. The 

 last two chapters, on electrical safety valves and light- 

 ning conductors, are particularly good. J. P. 



LETTERS TO THE EDITOR. 

 [The Editor docs not hold himself rest>onsiblc for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond 7villi the luriters of, rejected 

 manuscripts intended for this or any other part of Nature. 

 So notice is taken of anonymous <:oiiiiiiu»iValioii5.] 



On the Relation o "Recoil'' Phenomena to the 

 Final Radio ctive Product of Radium. 

 Is llic course of some experiments made by Miss Brooks 

 (Nature, July 21, 1904, vol. Ixx., p. 270) on the active 

 deposits from radium, it was found that the active product, 

 radium B, escaped in some manner from a body which 

 had been rendered active in the presence of radium' emana- 

 tion, and was carried at low pressures to the walls of the 

 ront:iininf; vessel. In his interpretation of this result, 

 Rutherford (" Radio-activity," p. 31)2) suggests the possi- 

 l^lity of the phenomenon belnR dui- to a recoil elTcil r.nther 

 •■^ n to a volatility possessed by the product radium B. 

 NO. 2069, VOL. 80] 



Radium A atoms, in breaking up, arc known to emu 

 o particles with a velocity of i-yxio' cm. per sec, and 

 as the mass of the a particle is 4 (H=i) and that of the 

 radium B atom approximately 200, it is clear from the 

 explosive nalure uf the disintegration of the radium .\ 

 atoms that Ihc radium B atoms must be hurled away 

 with a considerable velocity in directions opposite to those 

 in which the a panicles arc projected. 



Recent papers by Otto llahn and Lise Meilncr {Vcrh. 

 der deut. phys. Ges., xi., Jahr No. 3, and J'hys. Zeil., 

 10 Jahr, p. 81) and by Russ and Makower (I'roc. Roy. 

 Soc, No. 5, 553, p. 205, May 6) contain descriptions of 

 ex|X'riments which confirm the truth of Rutherford's 

 explanation, and also show that it is possible to isolate 

 the radio-active products, radium A, B, and C, thorium D 

 and actinium X and C, through the agency of this recoil 

 action alone. 



Other examples of this recoil phenomenon are also con- 

 tained in the recent experiments of Debierne {l.e Radium, 

 .■\pril) and in those of Kennedy on the active deposit from 

 actinium {Physical Review, May}. 



In considering these examples of the recoil effect, the 

 question naturally arises of a possible connection between 

 ihis phenomenon and the final transmutation product of 

 radium. Radium G (polonium) is known to emit a rays, 

 and when deposited on plates of copper, as Logcman and 

 others have shown, to emit also a feeble i radiation. 

 From the illustrations which have been cited above it 

 seems clear that heri' also the recoil phenomenon should 

 manifest itself in Ibe projecting from such radium G 

 coated plates of atoms of the final radio-active product. 



Evidence of such projection has recently been obtained 

 in the physical laboratory at Toronto by Mr. \'. K. Pound. 

 In his experiments an insulated plate of copper. A, 

 approximately 3 sq. cm. in area, which was coated with 

 a deposit of radium (j, was placed in a highly exhausted 

 chamber facing a second insulated plate of copper, B. 

 The plate B was joined to an electrometer, and the elec- 

 trical charges which it acquired under various electric and 

 magnetic fields were observed. 



With moderate electric and magnetic fields results 

 similar to those of Logeman, Ewers, Aschkinass, and 

 others were obtained, and from the form of the charging 

 curves which were obtained in such circumstances it was 

 clear that at least three types of radiation were present and 

 exerted an effect of greater or less degree on the charge 

 acquired by the plale B, viz. : — (1) the o rays emitted by 

 plate .\ ; (2) easily absorbed J rays emitted by plate A : 

 and (3) an easily .ibsorbed secondary radiation emitted 

 by plate B, consisting of negatively charged panicles. 



With higher magnetic fields, however, an entirely new 

 phcnomcnoii appeared. With such fields, especially when 

 the plate A was charged to an increasingly high positive 

 potential, it was found possible gradually to increase the 

 positive charge acquired by the plate B. As such higher 

 magnetic fields were suflicient to prevent the secondary 

 radiation from leaving the plate B, and the high positive 

 potentials were sufficient to retain the 5 radiation on the 

 plate .^ without afiecting the a radiation, it seems evident 

 that the rise in ibe positive charge .acquired by the plate 

 B was due to the existence of a r.idiation of negatively 

 charged particles from the plate .\ which had hitherto 

 escaped detection, but which in these experiments were 

 deflected by the m.ignetic field. When the plate A was 

 neutral or negatively (barged, the application of the mag- 

 netic field failed to give any indication of the presence of 

 this radiation, but with the application of a potential of 

 Kio or 240 volts (positive) to the plate .\ it could be readily 

 brought into evidence. It is of interest to see, therefore, 

 that in this case ,1 positive electric field united with a 

 magnetic field was the means by which the radiation was 

 isolated. 



The experiments are being continued, and it is too early 

 at present to write more definitely regarding the new radia- 

 tion. It seems, however, highly probable that this radia- 

 tion can be attributed to the " rest-atoins " of the active 

 product radium G. I he expulsion of an a particle would 

 leave this rest-atom negatively charged. Such rest-atoms 

 would leave the plaie In all directions as a stream cf 

 negatively charged particles. They would be less penc- 



