529 



elevation of temperature, and by an ingenious contrivance obtained 

 a much closer approximation to the true heat. 



The first part of his New System of Chemical Philosophy will pro- 

 bably constitute the most durable monument of his scientific genius ; 

 in this small volume are condensed the results of many years' patient 

 thinking and of much laborious research ; those larger portions, 

 which are devoted to the measure of temperature and the theory of 

 specific heat, may still be studied with advantage, though they were 

 deemed by Dr. Dalton himself to have been in great part superseded 

 by the labours of MM. Petit and Dulong. The short concluding 

 chapter contains the first announcement of the atomic doctrine 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 neutralise 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 INI. Gay Lussac's precise experiments on 

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

 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. 



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 phenomena, 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- 



