Ill 



CHEMISTRY SINCE THE TIME OF DALTON 



JOHN DALTON AND THE ATOMIC THEORY 



SMALL beginnings have great endings sometimes. 

 As a case in point, note what came of the small, 

 original effort of a self -trained back-country Quaker 

 youth named John Dalton, who along towards the close 

 of the eighteenth century became interested in the 

 weather, and was led to construct and use a crude 

 water-gauge to test the amount of the rainfall. The 

 simple experiments thus inaugurated led to no fewer 

 than two hundred thousand recorded observations re- 

 garding the weather, which formed the basis for some 

 of the most epochal discoveries in meteorology, as we 

 have seen. But this was only a beginning. The sim- 

 ple rain-gauge pointed the way to the most important 

 generalization of the nineteenth century in a field of 

 science with which, to the casual observer, it might 

 seem to have no alliance whatever. The wonderful 

 theory of atoms, on which the whole gigantic struct- 

 ure of modern chemistry is founded, was the logical 

 outgrowth, in the mind of John Dalton, of those early 

 studies in meteorology. 



The way it happened was this: From studying the 

 rainfall, Dalton turned naturally to the complementary 

 process of evaporation. He was soon led to believe that 



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