536 Sir J. J. Thomson on the Structure of 



be accommodated in the eight cells. To do this the contact 

 between one or more of the cells must be altered ; to find 

 room for the new electron one of the three electron contacts 

 must be reduced to a line contact, i. e. two of the cells must 

 have only an edge in common instead of the triangular face 

 which formed their interface before the new electron was 

 introduced. But if one cell moves so that it opens out the 

 contact with the cell on its left from a three- to a two-electron 

 contaet, it will also alter its contact with the cell on the 

 right, unless this moves also, and reduce this also to a 

 two-electron contact ; hence the system will be unsaturated 

 unless another electron is introduced to fill up the gap 

 caused by the loss of a contact. To supply this electron 

 another atom of hydrogen must be introduced. Hence we 

 see that the addition of the hydrogen atoms must occur in 

 pairs, and unless there is a movement of more than one cell 

 throughout the chain these pairs must be on adjacent carbon 

 atoms ; if one half the ring were to move as a rigid body past 

 the other half, the pairs would be on opposite carbon atoms. 

 These conclusions are borne out by j;he study of the addi- 

 tive compounds of benzene. 



Fig. 12. 



When there are two rings, as in naphthaline Ci H 8 , there 

 will be 10 cells and 48 electrons ; this would correspond 

 to an arrangement like that in fig. 12, where the two cells 

 round the two central carbons have two-electron contact, 

 while the ten contacts between the outer cells are three- 

 electron ones. 



The view that the electrons in a molecule are arranged in 

 sets of eight forms the basis of the very interesting papers 

 on chemical combination recently published by Professor 

 Lewis and Mr. Langmuir, their view as to the origin of these 

 sets differs from that given in this paper. 



We shall now turn from the chemical side of the theory to 

 the physical one, and consider how far its consequences are 

 in accordance with our knowledge of the physical properties 

 of atoms and molecules. As positive ray analysis is the most 



