A HISTORY OF SCIENCE 



to a single atom of oxygen), then the relative weights 

 of the original masses of hydrogen and of oxygen must 

 be also the relative weights of each of their respective 

 atoms. If one pound of hydrogen unites with five and 

 one-half pounds of oxygen (as, according to Dalton's 

 experiments, it did), then the weight of the oxygen 

 atom must be five and one-half times that of the hydro- 

 gen atom. Other compounds may plainly be tested in 

 the same way. Dalton made numerous tests before he 

 published his theory. He found that hydrogen enters 

 into compounds in smaller proportions than any other 

 element known to him, and so, for convenience, deter- 

 mined to take the weight of the hydrogen atom as 

 unity. The atomic weight of oxygen then becomes 

 (as given in Dalton's first table of 1803) 5.5; that of 

 water (hydrogen plus oxygen) being of course 6.5. The 

 atomic weights of about a score of substances are given 

 in Dalton's first paper, which was read before the Lit- 

 erary and Philosophical Society of Manchester, October 

 21, 1803. I wonder if Dalton himself, great and acute 

 intellect though he had, suspected, when he read that 

 paper, that he was inaugurating one of the most fertile 

 movements ever entered on in the whole history of 

 science ? 



Be that as it may, it is certain enough that Dalton's 

 contemporaries were at first little impressed with the 

 novel atomic theory. Just at this time, as it chanced, a 

 dispute was waging in the field of chemistry regarding 

 a matter of empirical fact which must necessarily be 

 settled before such a theory as that of Dalton could 

 even hope for a hearing. This was the question whether 

 or not chemical elements unite with one another always 



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