Manchester Memoirs, Vol. Iv. (191 1) No. %1t. 7 



man. As mentioned in the fifth paper of this series, he 

 confessed that he and Sidgwick once passed along a 

 valley without observing signs of glacial action, which 

 were, none the less, present everywhere. They failed to 

 perceive these signs because they were directing their atten- 

 tion to something else. In the same way the atomic 

 theory may be in Higgins' book even though Thomson 

 failed to perceive it. 



As a result of the controversy, it appeared that most 

 chemists were unable to deny Higgins' claims. William 

 Hyde Wollaston observed that Mr. Higgins " in his con- 

 ception of union by ultimate particles clearly preceded 

 Mr. Dalton in his atomic views of chemical combination." '^ 

 Thomas Graham, again, in his " Chemical Catechism," 

 puts the question, " Who first made use of the atomic 

 hypothesis in chemical reasonings ? " The answer is : — 

 " A Mr. Higgins, of Dublin — in a book of his published 

 in the year 1789."^ 



Again, it is true that William Higgins has been 

 almost forgotten. After his death, in 1825, he gradually 

 passed out of notice and recollection. The claims of 

 Dalton, on the other hand, have been advocated by a 

 succession of Manchester chemists, including W. C. Henry, 

 R. Angus Smith, and Roscoe and Schorlemmer. These 

 writers have thought to advance their cause by disparaging 

 Higgins, but, as I have shown in the third paper of this 

 series, their criticisms are unfair, and must be set aside. 



As I have already said, inasmuch as the " Daltonian 

 principle, a definite molecule for each substance," is the 

 principle also of Higgins' theory of the year 1789, there 

 is no avoiding the conclusion that Higgins forestalled 



^ Phil. Trans., 1814, p. 5. 

 ^ "Chemical Catechism," 1829, p. 35. 



