Bartow—A Mechanical Cause of Homogeneity of Crystals. 687 
distance separating them increases beyond a certain limit the 
mutual repulsion falls very rapidly either to zero or to a com- 
paratively low value. The position of this limit to depend on the 
nature of the particles and the conditions affecting them at the 
moment. 7 
5. A general force of compression’ to be applied to every 
assemblage of particles so as to limit the space allotted to it. 
6. Every assemblage of particles to be capable of passing into 
a state in which movement of some or all of the particles with 
respect to one another is so restricted as to be almost negligible; 
in other words, into such a state as would be produced by con- 
necting some or all of the particles closely contiguous to one 
another by very slightly elastic strings drawn straight, similar 
lengths being employed to connect similar pairs of particles. And 
such a change of state may or may not be accompanied by a 
change in the mutual repulsions exercised by the repellent par- 
ticles; and the latter change, if there be one, may consist in an 
increase or a decrease of these repulsions. 
And every assemblage thus changed to be capable of passing 
partially or entirely out of this state of restricted movement back 
to the condition in which the movement is unfettered.? And the 
connection established between the particles is to be regarded 
strictly as a property of their conditions, and as enduring 
only so long as the conditions capable of producing it endure, 
so that a fluctuation of the conditions might produce alternate 
tying and untying of the links connecting the particles of an 
assemblage. 
7. All assemblages of particles are supposed to be continually 
exposed to small (inconsiderable) local passing disturbances ade- 
quate to displace any equilibrium which is not the most stable 
1 Any other restraint or attraction which, while preventing indefinite expansion, 
permits the interaction of the mutual repulsions, will do equally well. Compare 
Boscovich, ‘‘ Theoria Philosophie Naturalis redacta ad unicam legem virium in natura 
existentium.’’ Where ail space is occupied by particles sufficiently near together to repel 
one another, no restraining force besides inertia may be necessary. 
2 This investigation does not throw any light on the causes or nature of change of 
state, or the causes of change of volume of matter, but merely premises that such changes 
of the assemblages of particles as are here defined can be brought about, and traces some 
of the effects consequent on these changes. 
SCIEN. PROC. R.D.S., VOL. VIII., PART VI. 3D 
