30 
POPULAR SCIENCE REVIEW. 
planes transverse to the line of pressure. If the conditions 
exclude even such change as this, the indestructible force may 
develope itself in other ways still less intelligible to us, and 
reappear as heat, chemical action, or segregation. Into these 
inquiries we need not now enter. Our W of limestone is ex- 
plained — that is, brought into an intelligible relation with 
other observed phenomena. 
It would be interesting, though hardly profitable, to pursue 
this subject yet further into the field of molecular philosophy. 
Many attempts have been made to resolve various physical 
states into combinations of certain hypothetical atomic forces. 
These speculations are sure to recur, and molecular or atomic 
theory will some day be the basis of all physical science. 
Newton, as he says, strongly suspected that all the pheno- 
mena of cohesion and aggregation, all the phenomena of 
chemistry and physiology, resulted from the agency of forces 
varying with the distance of the particles. Boscovitch en- 
deavoured to establish a general theory of cohesion upon the 
properties of unextended atoms endowed with powers of attrac- 
tion and repulsion varying not only in degree but kind with 
the distance, and to such elementary forces he expected ulti- 
mately to reduce the peculiar manifestations of chemical and 
vital change. In our day Sir William Thomson, expanding a 
suggestion made by Helmholz, has sought to show that all 
material phenomena may be due to motions created in an 
incompressible, frictionless, universal fluid — that the ultimate 
analysis of matter will hereafter give not particles, but 
vortices. As yet these doctrines remain mere unverified 
conjectures ; the atomic history of the universe is yet to be 
constructed. We do not accurately know what takes place 
when a piece of india-rubber is bent or a piece of moist clay 
squeezed into a new shape. Still we are in the way of pro- 
gress when we collect and sift facts, arrange them into classes 
under general propositions, and test those propositions by 
applying them to fresh cases. Hereafter it will be possible 
to apply one principle to explain at once the fluidity of water 
and the contortion of rocks. Even now we can group together 
the past and the present, the great and the small. We can 
show that the forces which curved round the Silurian rocks of 
Wales are still operative, and that the same forces can be dis- 
played and recognised in the laboratory of the student. 
