153 
matter, or of the exertion of any forces by it, excepting 
such as are open to direct experiment and observation. If 
there be any recondite forces that sustain the variable forms 
of bodies, all we can know about them must be derived 
from the sensible properties of matter; for any assumed 
properties, or motions of bodies, or their component parts, if 
hidden from our powers of perception, they are so because 
they afford no tests, by weight or measure, of their 
existence as physical realities. Still, with a view to obtain 
some conception of the laws that govern the visible and 
tangible forms of bodies, several hypotheses have been 
suggested to account for phenomena attending the muta- 
tions of bodies. It has been assumed that certain internal 
motions and forces are called into action by the changes 
that take place in the visible forms of bodies — to explain 
these we have had the theories of atoms , of corpuscules, of 
molecules and the like. By these theoretic views of the 
composition of bodies, the smallest particles in them are 
supposed to be endowed with functional properties , which 
exert mechanical forces, according to the distances apart of 
the atoms and molecules, in all ponderable bodies. The 
author does not object to these theories, if they may in 
anywise serve to clear the paths of inquiry into the 
physical properties of bodies and their mutations; but 
whatever may be the real or ideal internal action of the 
particles of matter upon each other, or upon their masses, 
the questions they involve do not admit of any solution, or 
even elucidation, by any course of mathematical investiga- 
tion that has been or can be applied to them, and this for 
the obvious reason that those particles (whether called 
atoms, molecules or otherwise) can have no conceivable 
weight or extension apart from their masses, and therefore 
no functional value can be assigned to them as the basis of 
any kind of moveable or statical forces in them. Whether 
such atoms and molecules be considered as in a state of 
