648 



SCIENCE 



[N. S. Vol. XXX. No. 775 



Since the maxima of Eotifera and Ento- 

 mostraca were coincident with or followed 

 closely those of the chlorophyll-bearing or- 

 ganisms upon which they fed, the author 

 reaches the conclusion that the factors which 

 controlled the periodic growths in the food 

 organisms would account for the rhythmic 

 phenomena in the total plankton. If some ob- 

 servations made by Knauthe which seem to 

 indicate that moonlight increases the photo- 

 synthetic activities of chlorophyllaceous or- 

 ganisms, and consequently their growth, be 

 accepted, then Professor Kofoid thinks that 

 this recurrent factor of the environment may 

 account for the rhythmic growth of these or- 

 ganisms which results in the production of 

 maxima each month at or near the time of 

 full moon. It may be said, however, that the 

 effect of moonlight on photosynthesis must 

 receive further confirmation before it can be 

 regarded as a factor of appreciable impor- 

 tance in the production of these phenomena. 



These studies show that the Illinois River 

 possesses an abundance of plankton material 

 which will serve as food for the higher or- 

 ganisms, and this abundant supply of food 

 material doubtless bears a very important re- 

 lation to the large production of food fishes 

 for which this stream is noted. It is also in- 

 teresting to know that plankton work was re- 

 cently resumed on this river after an inter- 

 ruption of ten years.' 



C. JUDAY 



Madison, Wis. 



The Theory of Valency. By J. Newton 

 Friend. London and New York, Longmans, 

 Green & Co. Pp. xiv + 180 ; crown 8vo, 

 cloth. Price, $1.60. 



This little volume is the latest addition to 

 the series of " Text-books of Physical Chem- 

 istry " edited by Sir William Eamsay. The 

 first thirteen pages are of the nature of an 

 historical introduction. This is followed by 

 thirty-eight pages devoted to the theory of 

 valency, valency and the periodic law, the 

 valency of carbon, and Thiele's theory. Ten 



' Science, Vol. XXX., p. 55. 



further chapters covering sixty-nine pages are 

 then devoted to a somewhat detailed discus- 

 sion of the valency of the elements contained 

 in each of the groups of the periodic system. 

 Finally, forty-three pages are taken up in the 

 consideration of Werner's theory, electro- 

 chemical theories, and the physical cause and 

 nature of valency. The chapters on the 

 valency of the elements of the various groups 

 of the periodic system are rather tedious read- 

 ing, and frequently lack completeness and 

 adequacy. Many of the statements and ex- 

 planations they contain would certainly be 

 challenged by chemists. But it must be re- 

 membered that the subject of valency has ever 

 been warmly debated, and it is hardly to be 

 expected that a brief resume of it would meet 

 general approbation. In the study of the com- 

 pounds of carbon and also in the investiga- 

 tion and correlation of many other compounds, 

 particularly the simpler ones, the theory of 

 valency has been of inestimable value, and the 

 book does give the reader this impression cor- 

 rectly. On the other hand, in the discussion 

 of variable valency, and the matter of partial 

 valencies, the author has not always been 

 clear. The reader is here left with the idea 

 that these portions of the subject are rather 

 more hazy and indefinite than they actually 

 are. The introduction and the discussion of 

 the various theories of valency form by far 

 the best portions of the book. It is somewhat 

 peculiar that the theory of valency should 

 have been chosen as the subject of a volume of 

 a series of books on physical chemistry, for 

 valency has always been considered as be- 

 longing to chemistry proper. As Dr. Friend's 

 book is the only attempt of an exhaustive, 

 systematic treatment of the subject of val- 

 ency, it will no doubt be useful to mature 

 readers who can read it critically. The vari- 

 ous references given, though they are far from 

 complete, will nevertheless serve very well to 

 introduce students to the literature of the 

 subject. 



The print, paper and binding of the book 

 are excellent, these features being similar to 

 those of the other volumes of the series. 



Louis Kahlenberg 



