26 PRESIDENT’S ADDRESS—SECTION A. 
matter (0), his theory being that atoms were purely geometrical 
points, or rather centres of force, having definite position in 
space, and capable of moving continuously therein, but possess- 
ing, however, mass preperties—.e., force was necessary to pro- 
duce change in their motion—incapable, however, of absolutely 
coinciding in space since, though at ordinary distances 
they attracted each other, at molecular distances they 
ultimately repelled one another with a force which in- 
creased without limit as their mutual distance diminished 
without limit. The theory is of note as an attempt at a 
purely monistic view of the universe. How far the notion 
of geometrical points possessing mass, and acting upon each 
other at a distance, may be said to be intelligible (p) is a 
question not easy to answer. Anyone holding “such a theory 
must, it is presumed, regard such functions as ultimate and in- 
explicable, otherwise [or in any case?] they are pure abstractions. 
Boscovich’s theory is not peculiar in this respect, for every other 
is finally involved in difficulties of the same order. It is worthy 
of note that it furnished a foundation for an elastic theory of 
what are now called, at the suggestion of Cauchy, isotropic 
solids. In 1821 Navier (7), and almost immediately afterwards 
Poisson (r) and Cauchy (s) developed expressions for the inter- 
molecular stresses, which are set up by the alteration of mole- 
cular configuration through external agency, 7.e. co say by im- 
pressed forces. Later, viz., in 1827, Cauchy rejected as incon- 
sistent the analysis of Navier and Poisson, and during that and 
several subsequent years developed Boscovich’s theory to its 
furthest limit. But the part played in the theory of elasticity 
by the conception of Boscovich, involving as it does the work of 
some of the most brilliant mathematicians in France, Germany, 
and England, is a story we must pass. 
18. D. Bernoulli and the Kinetic Theory of a Gas.—Another 
early and important application of the atomic conception was by 
Daniel Bernouilli (¢) in his Hydrodynamica, published in 1738. 
Bernouilli theoretically deduced Boyle’s law, empirically observed, 
from the assumption that the pressure exerted by any gas on its 
containing envelope was due to the impact of its particles (w). 
He must be regarded, therefore, as the real founder of the kinetic 
theory of gases. 
(0) Theoria philosophiz naturalis, redacta ad unicam legem virium in natura existen- 
tium. Vienna, 1758. 
(p) In physical theories, and for the purposes of physical science, the word intelligible 
seems to be equivalent t» ‘‘ mechanically representable,’’ or ‘* picturable. 4 
(q) [1785 - 1836]. 
(v) [1781—1840}. 
(s) [1789—1857]. 
(t) [1700—1782}. 
(uw) The kinetic energy relation to > pressure and a expressed by the equation, 
=4mu’ = 2p 
is equivalent to saying that the sum of the mass of each particle multiplied into the 
square of its velocity is equal to three times the product of the pressure and volume. 
