CH. xv.] CONSTITUTION OF ATOM 151 



is at present, it is worthy of some attention from its 

 own intrinsic interest. It will be found developed by 

 Professor J. J. Thomson in the Philosophical Maga- 

 zine for Dec. 1903 and March 1904; and a general 

 idea of its main features can be gathered from his 

 American " Silliman Lectures," published in 1904 by 

 Constable as a book called Electricity and Matter. 



Were it less hypothetical a further account of it 

 would be given here, but an extremely recent paper 

 by the same great Physicist has tended to reduce the 

 whole subject to a state of exaggerated uncertainty; 

 since he gives reasons, which appear to be sound 

 ones, in the Philosophical Magazine for June 1906, 

 for assuming that only one active electron is contained 

 in a hydrogen atom, and that all other elements contain 

 a number of electrons comparable to their atomic 

 weight, reckoned on the basis that H = 1 (see 

 Appendix L). This is an extraordinary and un- 

 suspected result, and at first sight appears very 

 unlikely, since the ordinary chemical assumption of 

 a unit atomic weight for Hydrogen has always been 

 known to be a pure convention, made for convenience 

 alone, and not likely to correspond with anything in 

 nature. I do not suppose that anyone imagined 

 that it would, even provisionally, be found to have 

 a physical and rational basis. The subject is further 

 referred to in Chapters XVII. and XIX. below. 



In that state of uncertainty the matter must be 

 left for the present ; but we may go on to indicate 

 roughly how some of the known properties of matter 

 could be expected or explained, on a view of the 

 electrical constitution of matter which supposes it 

 composed of a large number of positive and nega- 

 tive electric charges, irrespective of the particular 

 mode of their aggregation and distribution. 



