260 Prof. J. J. Thomson on the 
consider the series of arrangements of the corpuscles given on 
p- 258, in all of which the outer ring contains 20 corpuscles. 
An outer row of 20 corpuscles first occurs with 59 corpuscles ; 
in this case the number of corpuscles inside is only just 
sufficient to make the outer ring stable; this ring will there- 
fore be on the verge of instability, and when the corpuscles 
in this ring are displaced the forces of restitution urging 
them back to their original position will be small. Thus when 
this ring is subjected to disturbances from an external source, 
one or more corpuscles may easily be detached from it; such 
an atom therefore will easily lose a negatively electrified cor- 
puscle, and thus acquire a charge of positive electricity; 
such an atom would behave like the atom of a strongly 
electropositive element. When we pass from 59 to 60 cor- 
puscles the outer ring is more stable, because there is. 
an additional corpuscle inside it; the corresponding atom 
will thus not be so electropositive as that containing only 
59 corpuscles. The addition of each successive corpuscele 
will make it more difficult to detach corpuscles from the 
outer ring, and will therefore make the atom less electro- 
positive. When the stability of the outer ring gets very great,. 
it may be possible for one or more corpuscles to be on the 
surface of the atom without breaking up the ring ; in this. 
case the atom could receive a charge of negative electricity, 
and would behave like the atom of an electronegative element. 
The increase in the stability of the ring, and consequently in 
the electronegative character of the atom, would go on 
increasing until we had as many as 67 corpuscles, when the: 
stability of the outer ring would be at a maximum. A great 
change in the properties of the atom would occur with 68 
corpuscles, for now the number of corpuscles in the outer 
ring increases to 21; these 21 corpuscles are, however, only 
just stable, and would, like the outer ring of 20 in the 
arrangement of the 59 corpuscles, readily lose a corpuscle 
and so make the atom strongly electropositive. 
The properties of the groups of 59 and 67 corpuscles, which 
are respectively at the beginning and end of the serieswhich has. 
an outer ring of 20 corpuscles, deserve especial consideration. 
The arrangement of corpuscles in the group of 59, although 
very near the verge of instability, and therefore very lable 
to lose a corpuscle and thereby acquire a positive charge, 
would not be able to retain this charge. For when it 
had lost a corpusele, the 58 corpuscles left would arrange 
themselves in the grouping corresponding to 58 corpuscles 
which is the last to have an outer ring of 19 corpuscles; this 
ring is therefore exceedingly stable so that no further cor- 
