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XIV. The Atomic Theryru, in Rephi to Dr. Wrislit. 

 5y R. ^'. Atkixsox, F.C.S.-^ 



IT is exceediDgly gratilying to find that Dr. Wright gives a 

 practically nuqualified assent to the Atomic Theory. He 

 attempts to distinguish between the atomic hypothesis and the 

 atomic theory- j but when he defines a theory to be a proposition 

 the predictions of which are ■'•' mostly verified by experiment and 

 obseiwation/^ it will be seen that^ even according to his own de- 

 finition, the term theoi-y is more applicable than hypothesis to 

 Dalton's statement, ^ow, as he in no place attempts to criticise 

 what he terms the /'"atomic theory (as employed in University 

 College laboratory)/^ and as ir can be shown that this view is 

 merely a farther development of Dalton's original views, we may 

 fairly accept the weight of Dr. AVrighf's opinion in favour of the 

 theory. 



Dalcon represented elementary bodies as made up of an assem- 

 blage of globules, each of which consisted of a central atom of 

 solid matter suiTounded by an ataiosphere of heat. The only 

 difierence between this view and that now accepted by chemists, 

 apart from the difference in the theory of heat, is that they do 

 not commit themselves to any assertion as to the nature of this 

 central atom, — certainly not as great a modification as adopting 

 the mechanical in place of the material theory of heat, which no 

 one would regard as altering the main features of Dalton^'s con- 

 ception. Chemists treat such atoms in the same way as astro- 

 nomers treat the planets — that is, as practically indivisible, 

 although no astronomer would assert that they are in their na- 

 ture indivisible : the question is not raised. 



By his analysis of Dalton^s proposals into generalization, con- 

 vention, and hypothesis, Dr. TVright has not escaped from the 

 dilemma in which he was placed with regard to the combination 

 of elements in definite and multiple proportions. If this three- 

 fold division had been real, it would have afi'orded a very fair 

 means of escape ; but the three propositions are so inextricably 

 bound up together that it is not possible to separate any one 

 from the rest. Dr. T\'right represents ''^the quantitative com- 

 position of any homogeneous body .... by taking and compa- 

 ring simple multiples of certain fixed numbers attached respect- 

 ively to the name of each elementary substance occumng in the 

 body in question;"^ in other words, he attaches to a concrete 

 body a pure or abstract number; but under such circumstances 

 the number itself also becomes concrete, in which case the unit 

 to which it must be referred can only be a portion of the homo- 

 geneous matter to which it is attached. What benefit, then^ can 

 "^ Coramimicated bv the A-athor! 



