686 



SCIENCE. 



[N. S. Vol. I. No. 25. 



sheds, * * the cultivated will show the 

 steadiest conditions and the best-sustained 

 dry-season flows, but as between cultivated 

 and forested water sheds the forested will 

 produce the best results. * * It follows 

 also that floods will be most severe upon 

 barren areas." Hence there exists * * 

 ' the urgent necessity of preserving forests 

 upon slopes, and all areas which are not 

 adapted to agriculture ' (p. 348). 



Enough has been said to indicate the 

 scope of the volume; which can hardly fail 

 to become a hand-book on the question of 

 water supplj'. It is probably not too much 

 to say that this report alone is worth more 

 to the State of New Jersey than its geolog- 

 ical survey has ever cost. Other States of 

 dense population would do well to follow 

 the example of New Jersey, not only in 

 studj'ing their water resources, but in put- 

 ting the work under the direction of their 

 geological surveys; for the relation between 

 the geology of a region and the availability 

 of its water supplj^ is so intimate that no 

 other organization is better qualified to di- 

 rect the work. The U. S. G-eological Sur- 

 vey has work of this sort in progress in some 

 parts of the semi-arid regions of the West, 

 fi'om which good results are sure to come. 

 RoLLiN D. Salisbtiet. 



Univeesity of Chicago. 



John Dalton and the Rise of Modern Chemistry. 



By SiE Henry E. Eoscoe. New York 



and London, Macmillan & Co. 8vo. 



Pp. 216. Price, $1.25. 



It is one of the greatest achievements of 

 modern chemistry to have shown that for 

 each chemical element there is a measurable 

 quantity which, throughout all the trans- 

 formations that the element undergoes, re- 

 mains unchanged, and is, therefore, to be 

 regarded as a constant. The laws of defi- 

 nite, multiple and reciprocal proportions 

 of gas volumes and of specific heats, of mass 

 action and of the periodicity of properties, 



all give converging evidence that for each 

 element there is a definite constant quantity 

 which, in all the changes that the element 

 undergoes, acts like a unit. This constant 

 is the one unchanging, and, therefore, the 

 most characteristic property of the element. 

 The chemical and physical properties of an 

 element, its behavior under difierent con- 

 ditions, its possibility of undergoing change 

 under given circumstances, in short its 

 whole character, is dependent upon the 

 magnitude of this constant. A large part 

 of theoretical chemistry is taken up with 

 a consideration of the general methods that 

 are available for the determination of this 

 important quantitj', and it is customary to 

 express it by means of a number which in- 

 dicates its magnitude in terms of the 

 characteristic quantity of some one element, 

 usually hydrogen, taken as a unit. To 

 this number the name Atomic Weight has 

 been given, and to John Dalton, indispu- 

 tably, belongs the great credit of having 

 first introduced into chemistry the idea of 

 atomic weights. He transformed the New- 

 tonian corpuscular theory of the constitu- 

 tion of bodies into a workable chemical 

 hypothesis, and the subsequent develop- 

 m.ent of his idea, that the atoms of difierent 

 elements have difierent constant masses, 

 has given us our present system of atomic 

 weights. But, whether we associate with 

 this term the conception of an atomic con- 

 stitution of matter or not, the fact remains 

 that these constants stand to-day independ- 

 ent of any hypothesis, and are to be regard- 

 ed as mathematical quantities that can be 

 deduced from the general laws and princi- 

 ples of the science. 



In this book Sir Henry Eoscoe has given 

 us a most interesting account of the life and 

 work of the great Manchester chemist. 

 Dalton's life, like that of many scientific 

 workers, was not an eventful one, but he 

 was a man of marked personality, of posi- 

 tive traits of character, and our author has 



