366 



NATURE 



[August 20, 1903 



Among the Night People. By Clara Dillingham 

 Pierson. Pp. xi + 221. (London: John Murray, 

 1903.) Price 55. 

 This is an American book, for American children, and 

 about American nocturnal animals ; but, if we are not 

 mistaken, it will interest English children too, and 

 may be of no small value in letting them into some of 

 the secrets of the life of " the Night People " of the 

 world in general. It consists of a series of stories or 

 sketches of the doings of raccoons, musk-rats, skunks, 

 mice, weasels, foxes, moths, fireflies, &c., told with- 

 out any affectation in simple language, and with an 

 evidently real knowledge of the habits and character- 

 istics of these creatures, and with a gentle humour 

 which aptly conceals the instruction conveyed. The 

 animals are, of course, humanised to some extent, and 

 talk the language of human beings, but this is 

 managed with such skill, that the animal character- 

 istics are quite adequately retained. A good example 

 is the story of the inquisitive weasel, where a phleg- 

 matic black-tailed skunk is made to play with most 

 amusing effect on the lively curiosity of these little 

 animals, which are the same all the world over. The 

 illustrations of scenes in the dark, by Mr. F. C. 

 Gordon, are very happily conceived and executed. 



Qualitative Chemicai Analysis. By John B. Garvin, 

 B.S. Pp. viii + 241. (Boston:' Heath and Co., 

 1902.) Price 35. 6d. 

 It is rare in these degenerate days to find an enthusiast 

 for the teaching of qualitative analysis, who regards 

 it as "a source of joy to the majority of normal 

 minds," and as affording " the keenest delight and 

 satisfaction." For analysis, as it is taught, is usually 

 an arid tract, which the student is compelled to traverse 

 on the way to earning a grant or receiving a degree, 

 not a fertile country which he can cultivate with profit 

 and pleasure. Yet one is bound to confess that these 

 pages reflect the author's interest in his subject, and 

 leave the impression that, in the hands of such a 

 teacher, analysis might possess the attributes he 

 describes. This is effected by making the student dis- 

 cover and tabulate the reactions for himself._ Thus, 

 the mere mechanical following of directions is, 

 to a great extent, avoided, and the student is freed 

 from the burden of making his own observations 

 correspond with the printed information in his text- 

 book. For an elementary book the subject is very 

 fully treated. It is not intended to be used without 

 some assistance from the demonstrator, and conse- 

 quently many details of manipulation are suppressed. 



J. B. C. 



British Rainfall, 1902. Compiled bv H. Sowerby 

 Wallis and Dr. H. R. Mill. Pp. Ixxvi + 250. 

 (London : E. Stanford.) Price los. 

 This valuable work, which has appeared yearly since 

 i860, is perhaps better known to the scientific world 

 than any other work on meteorological subjects ; it 

 has become a unique and indispensable epitome of 

 reference on all questions relating to the distribution 

 of rain over the British Islands. Each year adds to 

 its importance, owing to the longer period over which 

 the averages extend, and the nearly constant addition to 

 the number of stations dealt with. These now amount 

 *o about 3500, and have increased 40 per cent, during 

 trte last fifteen years. It is highly creditable to the com- 

 pilers that they have been able to issue the volume 

 six months after the close of the year, within which 

 time every record has been carefully revised prior to 

 publication. In addition to the usual tables, the 

 present volume contains an exhaustive discussion of 

 the rainfall at Camden Square for the forty-five years 

 1858-1902, by Mr. H. Sowerby Wallis. Illustrations 

 and notes upon the unusual occurrences of the year 

 1902 greatly enhance the usefulness of the volume. 

 NO. 1764. VOL. 68] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



The Amount of Emanation and Helium from Radium. 



In connection with the very striking experiments de- 

 scribed by Sir William Ramsay and Mr. Soddy in Nature 

 of August 13, in which they have observed the presence of 

 helium in the gases obtained from radium bromide and 

 also the production of helium by the emanation of radium, 

 it may be of interest to give some calculations of the 

 probable amount of emanation and of helium produced by 

 radium on the disintegration hypothesis, recently put for- 

 ward by Mr. Soddy and myself to explain the phenomena 

 of radio-activity. 



A method of calculation has already been indicated by 

 us {Phil. Mag., May), but the data on which it was based 

 are somewhat imperfect. A more accurate estimate can 

 be made from the data of the amount of heat liberated by 

 radium, recently measured by Curie and Laborde. 



I have shown that the o or easily absorbed rays from 

 radium consist of a stream of positively charged bodies, of 

 mass about twice that of the hydrogen atom, projected 

 with a velocity of about 2-5x10^ cm. per sec. These re- 

 sults have been recently confirmed by Des Coudres. These 

 a bodies are expelled trom every part of the mass of radium, 

 but in consequence of the ease with which they are 

 absorbed, only a small proportion of them escapes into the 

 air. This self-bombardment of the radium probably gives 

 rise to a large proportion of the heat which keeps the 

 radium at a temperature above that of the surrounding 

 atmosphere. Assuming for the moment that all of the heat 

 is supplied by this continuous bombardment, an estimate 

 can readily be made of the number of o bodies projected 

 per second from one gramme of radium. 



The kinetic energy of each projected body is 5X10-^ 

 ergs. Since this energy is transformed into heat in the 

 mass of radium, the number of bodies projected to give 

 an emission of heat of 100 gr. cals. per hour — the amount 

 determined by Curie and Laborde — can be shown to be 

 2-4x10" per second. Now Townsend has shown from 

 experimental data that Ne = i-22 x 10'", where N is the 

 number of atoms in i c.c. of gas at standard pressure and 

 temperature, and e is the charge carried by an ion. The 

 latest value of e, found by J. J. Thomson, is 3-4x10-", so 

 that N=3-6x 10". 



If the a bodies after expulsion can exist in the gaseous 



form, the volume of the gas produced (at standard pressure 



^ . , 2-4x10" . , 



and temperature) is thus :jT6 ~j^=6-7X io-° c.c. per sec. 



or 0-2I c.c. per year. Allowing a wide margin for the 

 possibility that only one-tenth of the heat emitted by radium 

 is due to the kinetic energy of the projected bodies, the 

 volume of the a particles should lie between 0-021 c.c. and 

 0-21 c.c. per year for each gramme of radium. 



The determination of the mass of the a body, taken in 

 conjunction with the experiments on the production of 

 helium by the emanation, supports the view that the a 

 particle is in reality helium. In addition, the remarkable 

 experiment of Sir William and Lady Huggins in which 

 they found that the spectrum of the phosphorescent light 

 of radium consisted of bright lines, some of which within 

 the limit of error were coincident with the lines of helium 

 in the ultra-violet, strongly supports such a view. For as 

 a consequence of the violent expulsion of the a particle, it 



