IV. 



THE CONSTITUTION OF THE ATOM. 



By HAROLD A. WILSON, F.R.S. 

 (Read April 22, 191 1.) 



According to Sir J. J. Thomson's theory^ atoms may be regarded 

 as rigid spheres of positive electricity containing negative electrons 

 which can move about freely through the positive charge. The 

 total negative charge on the electrons in an atom is equal to the 

 positive charge on the sphere. This theory has many advantages 

 over the theory of Sir J. Larmor, who regards atoms as systems of 

 positive and negative electrons in rapid motion. In the first place 

 the sphere of positive electricity provides a rigid and stable founda- 

 tion which is lacking in the other theory and which seems very neces- 

 sary to explain the extraordinary stability of atoms. It is difficult to 

 see how Sir J. Larmor's atoms could possibly survive the shocks of 

 continual violent collisions with other atoms. 



Sir J. J. Thomson's theory has also the great advantage that it 

 explains the fact that only negative electrons can be isolated and that 

 positive electricity is always associated with atoms or molecules of 

 matter. 



It also explains the fact deduced from the Zeemann efifect that 

 spectral lines are emitted by vibrating negative electrons and not by 

 positive electrons. It is consistent with the fact that atoms can 

 lose a few negative electrons without their identity being destroyed 

 which does not seem possible on Sir J. Larmor's view. The kinetic 

 theory of gases agrees best with the facts when the atoms are re- 

 garded as rigid spheres which again is strongly in favour of Sir 

 J. J. Thomson's theory. 



This theory therefore may be used as a working hypothesis wdiich 

 enables a mental picture of the atom to be formed. It leaves the 

 nature of electricity and of the iether an open question and is conse- 



' " The Corpuscular Theory of Matter," IQ07. 



366 



