THE REIGN OF LAW 159 



most conduced to the end for which God formed 

 thorn." Dalton was so much under the influence of 

 the idea that the physical universe is made up of 

 these indivisible particles, or atoms, that his biogra- 

 pher describes him as thinking corpii&cularly. It is 

 probable that his imagination was of the visualizing 

 type and that he could picture to himself the arrange- 

 ment of atoms in elementary and compound substances. 



Now Dalton's master had taught that the atoms of 

 matter in a gas (elastic fluid) repel one another by 

 a force increasing in proportion as their distance 

 diminishes. How did this teaching apply to the at- 

 mosphere, which Priestley and others had proved to 

 consist of three or more gases? Why does this mix- 

 ture appear simple and homogeneous ? Why does not 

 the air form strata with the oxygen below and the 

 nitrogen above? Cavendish had shown, and Dalton 

 himself later proved, that common air, wherever ex- 

 amined, contains oxygen and nitrogen in fairly con- 

 stant proportions. 



French chemists had sought to apply the principle 

 of chemical affinity in explaining the apparent homo- 

 geneity of the atmosphere. They supposed that oxygen 

 and nitrogen entered into chemical union, the one 

 element dissolving the other. The resultant com- 

 pound in turn dissolved water ; hence the phenomena 

 of evaporation. Dalton tried in vain to reconcile this 

 supposition with his belief in the atomic nature of 

 matter. He drew diagrams combining an atom of oxy- 

 gen with an atom of nitrogen and an atom of aqueous 

 vapor. The whole atmosphere could not consist of 

 such groups of three because the watery partiolos 

 were but a small portion of the total atmosphere. 



