Jl'XE 21, 1895.] 



SCIENCE. 



687 



interwoven a description of the personal 

 characteristics of the man with an account 

 of liis scientific work and tlie incidents of 

 his life in such a way as to make a most 

 attractive and entertaining biography. 



From his early years Daltou was accus- 

 tomed to looking at things from the stand- 

 point of the atomic theory, and thi-oughout 

 his life he remained a firm supporter of this 

 doctrine. Like Newton, he conceived of 

 atoms as ' hard impenetrable, movable par- 

 ticles,' ' incomparably harder than any po- 

 rous bodies compounded of them, even so 

 very hard as never to wear or break in 

 pieces.' These atoms were supposed to be 

 surrounded with an atmosphere of heat. 

 He has left some drawings which show- 

 how he pictured to his mind the structure 

 of the smallest particles of compounds, and 

 in these he foreshadowed the modern con- 

 stitutional and stereo-chemical formulas. 

 In gases and clastic fluids he considered 

 matter to be in an extreme state of division, 

 and nearly all of his important discoveries 

 resulted from experiments upon gases. It 

 was by considering the constitution of gases 

 that he came to the idea of atomic weights. 



Dalton was not as skillful an experi- 

 menter as some of his contemporaries; most 

 of his apparatus was made by himself and 

 was often of a very primitive kind. It is 

 remarkable that he should have been able 

 to get the results with it that he did ; re- 

 sults that were in most cases confirmed l)y 

 other workers who used more accurate in- 

 struments and more exact methods. Some 

 of the important facts that he discovered 

 wei-e the equal expansibility of different 

 gases under the influence of heat : the prac- 

 tical constancj- of the composition of the 

 air, a fact which he established by n)eans of 

 a large number of analyses of air collecttd 

 at different places and at diflercnt alti- 

 tudes ; the law of partial pressures, or that 

 the total pressure of a gas mixture is equal 

 to the sum of the partial pressures of the 



components, and that in a mixture of gases 

 each component acts like a vacuum to tlie 

 other components and behaves as though it 

 alone were present. He also investigated 

 the solubilitj- of gases in liquids ; but his 

 greatest discovery was the law of multiple 

 proportions. Upon this discovery and upon 

 the fact that he introduced the atomic theory 

 with the idea of atoms of different weights 

 his great fame as a scientific man rests. 



Of especial interest in this book is the 

 account here published for the first time of 

 how Dalton arrived at his important con- 

 clusion. Among the Dalton papers belong- 

 ing to the Manchester Literary and Philo- 

 sophicial Society, Sir Henrj- Roscoe has 

 found some manuscript notes prepared by 

 Dalton for a course of lectures that he de- 

 livered at the Royal Institution in the win- 

 ter of 1809-10. These notes are printed 

 in full and give an account by Dalton him- 

 self how his ideas regarding the atomic 

 theory came to him. 



Mentally he was vigorous, independent 

 and self-reliant ; he gave little attention to 

 the results obtained by othei-s. Like New- 

 ton he reached his conclusions bj* quiet, 

 steady, continuous thinking. His long life 

 was spent in experimenting and reflecting. 

 It is pleasant to know that in his later years 

 many honors and tokens of esteem came to 

 him from his countrymen and from abroad. 



After Dalton the atomic theory was de- 

 veloped and put upon a much broader 

 foundation by Berzelius, and through his 

 work and that of a long line of illustrious 

 successor it has become the central domi- 

 nant feature of theoretical chemistry. 



It is noteworthy that Joule, who did so 

 much to establish the law of the conserva- 

 tion of energy, was a pupil of Dalton, and 

 that the names of both master and pupil 

 are so intimately associated with our two 

 great intellectual instruments of investi- 

 gating nature, the atomic liypothcsis and 

 the theory of energj'. The deductions of the 



