492 



SCIENCE 



[N. S. Vol. XXXVII, No. 952 



of children as affecting the digestion of their 

 food. It would be well if all parents could be 

 made to heed the author's suggestions in re- 

 gard to thoughtlessness in rebuking children 

 at the table and the almost cruel practise of 

 forcing them to eat what they dislike. The 

 statements that " there is an element of hy- 

 pocrisy in the attitude of parents who are se- 

 lecting precisely what they please to eat while 

 compelling little children to swallow food 

 which repels " and " to oblige a child to finish 

 a plateful of food against its inclination may 

 be crass brutality " are forceful and should be 

 heeded by those who have the care of the 

 physical development of children. 



The reader can but wish that the author had 

 been more free in the use of cuts, for those 

 which are given are very helpful. 



W. H. Jordan' 

 New York Agricdltukal 

 Experiment Station 



Studies in Radioactivity. By W. H. Bragg, 

 M.A., F.R.S. Macmillan. 1912. Pp. x + 

 196. $1.60. 



Physics owes to Professor Bragg two of the 

 most important of its recent advances. He 

 first conceived and successfully carried out ex- 

 periments on the " range " of corpuscular 

 radiations and on the " stopping power " of 

 different substances for these radiations. 

 These experiments, with those on scattering, 

 which inevitably followed, have been chiefly 

 responsible for such additions as have re- 

 cently been made to our knowledge of the in- 

 ternal structure of the atom. The first 10 

 chapters — 104 pages — of the book in hand are 

 taken up with a presentation in clear, non- 

 mathematical language, of the present status 

 of our knowledge of " range," " stopping 

 power," " scattering " and " ionization " as 

 these terms apply to the °- and P particles. 

 This material, culminating in C. T. E. Wil- 

 son's beautiful photographs of the tracks of 

 tt and /5 particles, probably marks the end of 

 the conception of the positive charge of the 

 atom as a uniform sphere of positive electrifi- 

 cation. It seems to demand instead some sort 

 of a Saturnian atom. 



Bragg's second important contribution has 

 consisted in the amassing of evidence for the 

 inter-convertibility of /3 rays and X rays, or 

 /3 rays and y rays. This evidence is presented 

 in the second half (pp. 104^-196) of his book, 

 which deals wholly with studies on the nature 

 of X and y rays. That this evidence is ex- 

 ceedingly convincing admits of no dispute, but 

 that it can be successfully interpreted in terms 

 of a neutral pair theory is more than doubt- 

 ful. Indeed so rapid have been the strides 

 made during the past year in establishing the 

 essential identity of X rays and light that I 

 fancy that Professor Bragg himself would to- 

 day interpret all his results in terms of an 

 ether pulse theory instead of a neutral doublet 

 theory, but it would have to be an ether 

 pulse theory of the J. J. Thomson sort, in 

 which the energy remains localized in space 

 instead of being distributed uniformly over 

 the wave front. For a clear statement of the 

 apparent necessity for some sort of a localiza- 

 tion of radiant energy in the wave front the 

 second half of Professor Bragg's book could 

 scarcely be excelled. One might wish that the 

 author had brought out more emphatically 

 the parallelism between the behavior of X 

 rays and ultraviolet light, for it is in this 

 parallelism that the chief argument against 

 the neutral doublet theory is found. 



The book is invaluable to every student of 

 the absorbing problem of the nature of radiant 

 electromagnetic energy. 



E. A. MiLLIKAN 



Univeesity or Chicago 



BOTANICAL NOTES 

 POLYSTICTUS VEESICOLOK AS A FOOD PLANT 



In the course of some investigations made 

 by Professor M. R. Gilmore in August, 1912, 

 on the knowledge and use of the indigenous 

 plants by the Dakota nation of Indians, the 

 economic botany of the Dakotas, he learned 

 of the use of Polystictus versicolor as a hu- 

 man food. The Dakota name is Cha" na" pa,'' 



^ The raised n signifies a vanishing sound some- 

 thing like the French n. 



