DISCOVERY BY MEANS OF INFERENCE. 599 



1*91 volumes of hydrogen. The idea that substances 

 unite together chemically in definite proportions by weight, 

 like that of all great scientific conceptions, began to be 

 inferred by several chemists, before it was proved and really 

 discovered ; it occurred to the minds of Higgins, Wenzel, 

 Proust, and Kichter. Higgins, having in 1789 stated 

 4 that in volatile vitriolic acid, a single ultimate particle 

 of sulphur is united to two of dephlogisticated air ' (i.e. 

 oxygen), and that, in perfect vitriolic acid, every single 

 particle of sulphur is united to two of dephlogisticated 

 air, being the quantity necessary to saturation,' drew 

 similar inferences concerning the compounds of nitrogen 

 and oxygen and the composition of water. But it was 

 Dalton who, by laborious study, experiment, and com- 

 parison of facts, chiefly proved the truth of the inference, 

 and really discovered the theory. By associating the 

 ancient notion of atoms with the modern conception of 

 definite chemical combination by weight, he gave a degree 

 of precision to the idea of an atom which did not pre- 

 viously exist, and enabled succeeding chemists to infer that 

 it is the smallest particle of a simple body, which can 

 chemically combine with another, and exist in a chemi- 

 cally combined state. Prout's inference and theory, that the 

 atomic weights of each of the elementary substances were 

 simple multiples of that of hydrogen, has not so well stood 

 the test of experiment. Stas has shown, by very rigidly 

 accurate investigations, that those of nitrogen, oxygen, 

 chlorine, bromine, iodine, silver, lithium, sodium, and 

 potassium do not conform to it. The theory that gases 

 chemically combine in definite proportions by volume as 

 well as by weight, was an inference drawn by Gay-Lussac, 

 about the year 1809, from the results of one of his re- 

 searches. In 1811, Amadeo Avogadro drew the further in- 

 ference, and in 1814 Ampere reproduced the theory, that 



