JOHNDALTON 167 



of matter bound together by a force of attraction, which is more or 

 less powerful according to circumstances, and which as it endeavours 

 to prevent their separation, is very properly called in that view, attrac- 

 tion of cohesion; but as it- collects them from a dispersed state (as 

 from steam into water) it is called attraction of aggregation, or more 

 simply, affinity. Whatever names it may go by, they will signify one 

 and the same power. It is not my design to call in question this con- 

 clusion, which appears completely satisfactory; but to show that we 

 have hitherto made no use of it, and that the consequence of the ne- 

 glect has been a very obscure view of chemical agency, which, is daily 

 growing more so in proportion to the new lights attempted to be 

 thrown upon it. 



The opinions I more particularly allude to, are those of Bertholet 

 on the Laws of chemical affinity ; such as that chemical agency is pro- 

 portional to the mass, and that in all chemical unions there exist insen- 

 sible gradations in the proportions of the constituent principles. The 

 inconsistence of these opinions, both with reason and observation, can- 

 not, I think, fail to strike every one who takes a proper view of the 

 phenomena. 



Whether the ultimate particles of a body, such as water, are all 

 alike, that is, of the same figure, weight, etc., is a question of some im- 

 portance. From what is known, we have no reason to apprehend a 

 diversity in these particulars : if it does exist in water, it must equally 

 exist in the elements constituting water, namely, hydrogen and oxygen. 

 Now it is scarcely possible to conceive how the aggregates of dissimi- 

 lar particles should be so uniformly the same. If some of the particles 

 of water were heavier than others, if a parcel of the liquid on any 

 occasion were constituted principally of these heavier particles, it must 

 be supposed to aflfect the specific gravity of the mass, a circumstance 

 not known. Similar observations may be made on other substances. 

 Therefore we may conclude that the ultimate particles of all homo- 

 geneous bodies are perfectly alike in weight, figure, etc. In other 

 words, every particle of water is like every other particle of water; 

 every particle of hydrogen is like every other particle of hydrogen, etc. 



