164 COEEELATION OF PHYSICAL FOKCES. 



heat. These experiments give a production of mechanical 

 work by chemical action, not, it is true, a direct production, 

 but, as the heat and work are in inverse ratios, and each has 

 its source in chemical action, they prove that they are definite 

 for a definite amount of chemical action, and as each is pro- 

 duced respectively by electricity and magnetism, these forces 

 must also bear a definite relation to the initial chemical force. 



The doctrine of definite combining proportions, which so 

 beautifully serves to relate chemistry to voltaic electricity, 

 led to the atomic theory, which, though adopted in its univer- 

 sality by a large majority of chemists, presents great difficul- 

 ties when extended to all chemical combinations. 



The equivalent ratios in which a great number of sub- 

 stances chemically combine, hold good in so many instances, 

 that the atomic doctrine is believed by many to be universally 

 applicable, and called a law ; and yet, when followed in the 

 combinations of substances whose natural chemical attractions 

 are very feeble, the relation fades away, and is sought to be 

 recovered by applying a separate and arbitrary multiplier to 

 the different constituents. 



Thus, when it was found that a vast number of substances 

 combined in definite volumes and weights, and in definite vol- 

 umes and weights only, it was argued that their ultimate 

 molecules or atoms had a definite size, as otherwise there 

 was no apparent reason why this equivalent ratio should hold 

 good : why, for instance, water should only be formed of two 

 volumes or one unit by weight of hydrogen, and of one vol- 

 ume or eight units by weight of oxygen ; why, unless there 

 were some ultimate limits to the divisibility of its molecules, 

 should not water, or a fluid substance approximating to water 

 in character, be formed by a half, a third, or a tenth part of 

 hydrogen, with eight parts of oxygen ? 



It was perfectly consistent with the atomic view that a 

 substance might be formed with one part combined with eight 

 parts, or with sixteen, or with twenty-four, for in such a sub- 



