172 



NA TURE 



[December 22, 1904 



•easy to show that we can never, in our beakers and 

 retorts, imitate the biochemical conditions of vital 

 synthesis as it is for a mathematician to prove the 

 transcendence of t. 



This view, like its opposite, is, however, in the 

 present state of our knowledge, rather a matter of 

 opinion than of proof. 



In conclusion we congratulate the author on having 

 produced a most useful work— a work of almost ultra- 

 German thoroughness— and one which will be an 

 immense boon to all interested in the subject with 

 which it deals. 



lONISATION AND ABSORPTIOS. 

 The Becqiierel Rays and the Properties of Radium. 

 By the Hon. R. j. Strutt. Pp. vii + 214. (London : 

 Edward Arnold, 1904.) Price 8s. 6d. net. 



A NUMBER of books dealing with radio-activity 

 and the kindred phenomena have already 

 appeared; and it is a bold thing on the part of an 

 author to place another before the public. However, 

 with the exception of Prof. Rutherford's inimitable 

 treatise on the subject, none of the previous works 

 have been characterised by any striking individuality, 

 so that there is, or rather was, still room for a 

 vigorous statement of the general features of the sub- 

 ject from a popular point of view. This the author of 

 the present work has accomplished in a manner that 

 leaves little room for criticism. He possesses to a 

 remarkable degree the faculty of stating difficult ques- 

 tions in a simple way, and of expressing the answers 

 in a language which is easily understood. 



In a book of this kind there is usually a good deal 

 of treatment which appears somewhat slipshod when 

 regarded from a strictly scientific standpoint ; but such 

 a charge cannot with justice be maintained against 

 the present volume. Naturally some of the most in- 

 tricate points, such as the effect of a magnet on a 

 moving electric charge, have to be treated analogically 

 to make them represent anything real to a mind in- 

 expert in dealing with this class of phenomena; but 

 here the author has not only been fortunate in choosing 

 -familiar instances, but those chosen have been true 

 analogies, and accurately represent the physical 

 features of the case. The whole treatment is char- 

 acterised by vigour and interest, and is such as we 

 should have ever\- reason to expect from the pen of 

 so well-known an investigator in this branch of 

 physical science as the author. 



It is scarcely necessary- to analyse in detail the con- 

 tents of the book, but the whole forms a clear and 

 concise presentation of the great question of the rela- 

 tionship between electricity and matter, which is of 

 overpowering interest to physicists at the present time. 

 In the first chapter we are made familiar with the 

 various phenomena accompanying electric discharge 

 in rarefied gases, and are thus placed in a position to 

 understand the working of what may be regarded as 

 a miniature discharge tube, viz. a radio-active atom. 

 After describing the various manifestations of radio- 

 activity and the properties of the radiations, the author 

 NO. 1834, VOL. 71I 



considers the various products of radio-active change. 

 We are thus led to a probable view of the mode of 

 origin of the chemical elements, in the evolution of 

 which the inert gases seem to form the final stage. 

 The last chapter forms a very lucid account of the 

 electrical theory of mass and the various views of 

 atomic structure based thereon. 



Unfortunately there is one serious blot on the 

 general excellence of the book, and that is the treat- 

 ment of absorption in chapter iv. Almost at the out- 

 set (p. S-), the author contradicts himself owing to 

 the word " greater " having crept in where he doubt- 

 less intended to say " less." This uncorrected error 

 is not likely to cause much trouble to those who are 

 familiar with the subject, but we imagine the beginner 

 will be greatly perplexed by tr3ing to reconcile this 

 statement with what follows. 



Apart from this, it seems a great pity that so much 

 stress should be laid on Madame Curie's experiments 

 on the absorption of the a-rays from polonium, as it 

 is doubtful what conclusion can be drawn from them 

 except that practically all the rays are stopped by 

 about four centimetres of air. In the experiments re- 

 ferred to a quantity of polonium was placed at a 

 variable distance below two parallel plates three centi- 

 metres apart. A hole in the lower plate covered by 

 wire gauze allowed the a-rays from the polonium to 

 penetrate the region between the two plates, and the 

 ionisation it produced there was taken to measure its 

 " intensity'." Madame Curie then investigated the 

 diminution in the ionisation produced by placing a 

 sheet of aluminium foil oooi cm. thick (equivalent to 

 2 cm. of air) over the lower plate, when the polonium 

 was at different distances below it. When the polo- 

 nium was 0-5 cm. away the aluminium cut down the 

 radiation to one-quarter its previous value, whilst 

 when the distance was iq cm. the ionisation was 

 reduced to one-twentieth. This shows clearly, as 

 Madame Curie pxiinted out, that 1 le o-rays which 

 have passed through a certain thickness of matter are 

 less penetrating than those which have not. The ques- 

 tion, however, which is of most interest in the present 

 state of the subject is how the ionisation per centi- 

 metre of path varies with the amount of matter pre- 

 viously passed through. These experiments furnish 

 no very certain answer to this question, since when 

 the aluminium foil is inserted the whole of the radia- 

 tion is absorbed long before it reaches the upper plate, 

 so that the different experiments are not strictly com- 

 parable. The whole question of absorption is very 

 intricate, and it is undesirable to dwell further upon 

 it here. There is still plenty of room for experimental 

 investigation on this subject. For instance, Town- 

 send's experiments on ionisation by collision and 

 Durack's on that produced by the Lenard and 

 Becquerel rays show that the number of ions pro- 

 duced per cm. by a moving corpuscle increases with 

 the velocity up to a certain point, and then decreases. 

 It would be of interest to see whether, as is probably 

 the case, this holds for the positively charged o-rays 

 as well. 



The book contains three useful appendices. The 

 first describes a number of simple experiments illus- 

 trating the essential features of radio-activity ; the 



