706 
Proceedings of Royal Society of Edinburgh. [sess. 
figuration of equilibrium to another, and back ; as, for instance, the 
two configurations of § 46 (footnote) below. The group may still 
retain its form as a solid, and something of its rigidity as a solid. 
§ 42. Now reverse the operations at the boundary so as to diminish 
the inter-atomic oscillatory energy of the group. The atoms may 
fall back into their previous positions of equilibrium. But they 
may not ; and instead they may fall into another configuration 
more readily taken in a settlement from internal agitation than the 
previous configuration which was arrived at by growth from the bound- 
ary. This (with true molecules of matter instead of the ideal Boscovich 
atoms) seems to me, without doubt, the explanation of Madan’s* 
beautiful discovery regarding chlorate of potash, and the change of 
crystalline structure, by which Lord Bayleighf has shown that the 
optical phenomena presented in it are to be explained. Virtually 
the same view to explain other changes of crystalline structure by 
differences of temperature or applications of pressure seems to have 
been given by M. Mallard, J who is quoted by Madan in the article 
above referred to. In a future communication to the Royal Society 
I hope to include considerations regarding the effect of inter-atomic 
forces and motions in guiding to one or other of the two configura- 
tions described in § 54 and footnote on § 46 below. 
§ 43. Once more communicate and continue communicating energy 
to the group by forces applied directly to its constituent atoms, and, 
at the same time, keep introducing fresh atoms from the outer 
boundary into the atmosphere surrounding the group to prevent the 
number of atoms in the group from diminishing. The intestine com- 
motion will become so great that all configurations of equilibrium 
are utterly departed from, but still the atom is surrounded by neigh- 
bours well within the region of its attractive influence (a shell 
bounded by two concentric surfaces of radius I and £ respectively) 
and constantly crossing and recrossing the spherical surface of radius 
£, or into and out of the sphere of repulsive force. If the region of 
attractive force be sufficiently thick, and the augmentation of the 
repulsive force from zero towards infinity be sufficiently rapid, it is 
* “On the Effect of Heat in Changing the Structure of Crystals of Potassium 
Chlorate,” Nature, May 20, 1886. 
t Philosophical Magazine, 1888. 
+ Bulletin de la Societe Mindralogique , 1882, and December 1885. 
