Royal Society. HI 



chapter contains the first announcement of th6 atoWiib dOcrtrine of 

 chemical combination. 



"'He has often expressly stated that the tables of chemical equiva- 

 lents constructed by Wenzel and Richter first suggested to him the 

 conception that chemical combination must have place between the 

 ultimate particles or indivisible atoms of bodies. The tabulated 

 differences of weight of the different bases required to neutralize a 

 given weight of acid would, on this hypothesis, represent the respec- 

 tive weights of their ultimate atoms. Further evidence of more 

 decisive character presented itself in the instances in which one body 

 combines with another in more than one proportion. The successive 

 combining quantities were ascertained to be represented by numbers 

 that were simple multiples of the smallest or lowest quantity. Dr. 

 Dalton's earliest illustration of his law of multiple proportions was 

 derived from the gaseous compounds of oxygen and nitrogen. Dr. 

 WoUaston afterwards discovered other examples of the law in the 

 tartrates and oxalates, and M. Gay Lussac's precise experiments on 

 gaseous combination completed the chain of evidence. All the phse- 

 nomena of inorganic chemistry have been since shown to be in strict 

 accordance with the atomic hypothesis, which has banished the un- 

 certainty of conflicting results, by enabling the experimentalist to 

 anticipate and correct his analyses, and has thus raised chemistry, as 

 respects numerical precision, almost to the rank of a mathematical 

 science. ' -'''■'f'-^'- ' ■•>■ ■ ■;■'!:■■•■ ■' ' i" * 



It would be inconsistent with the principles of logical induction to 

 claim for the atomic doctrine higher rank than that of the most con- 

 venient form of expressing and recording chemical phaenomena, and 

 of the most probable hypothesis that has been hitherto proposed for 

 interpreting chemical combination. In the field of organic analysis, 

 which has of late years been laboured with signal success, rules of 

 combination seem to obtain which are difficultly reconcileable with 

 the doctrine of Dalton. It is scarcely possible to conceive the me- 

 chanical juxtaposition of so large a number of elementary atoms as 

 would appear to constitute one compound organic atom ; there are 

 consequently many among the cultivators of this branch of chemical 

 science who refuse to accept the atomic hypothesis as now consti- 

 tuting a sufficient generalization of established facts. Yet even in 

 the chemistry of vegetable substances, the remarkable changes dis- 

 covered by Mitscherlich, which he conceives best explained by the 

 union of propejacent atoms of hydrogen and oxygen, and their elimi- 

 nation in the form of water, minister strong support to the theory of 

 atomic combination. Without venturing to anticipate the future 

 destinies of the hypothesis of Dalton, it is sufficient for the fame of 

 its author to acknowledge the mighty impulse it has given to the 

 progress of chemical knowledge. 



Dr. Dalton died on the 27th of July, 1844. 



Thomas Henderson, Professor of Practical Astronomy in the 

 University of Edinburgh, and Her Majesty's Astronomer for Scot- 

 land*. 



* A full memoir of Professor Henderson, from the Proceedings of the 

 Astronomical Society, will be found at p. 60 of the present volume.— Ed. 



