Tramactiom of the Cambridge Philosophical Society* 69 
which value, in the case of reflection from water at the- proper angle, 
is part of the intensity of the incident wave. This minimum 
value increases rapidly as the index of refraction increases ; and 
thus the quantity of light reflected at the polarizing angle becomes 
considerable for highly refracting substances ; a fact, which has 
been long known to experimental philosophers. 
In Mr. Earnshaw’s memoir the Eetherial medium is treated as a 
system of detached particles ; and he is led by his investigations 
to various conclusions, of which the most important are, that the 
molecular forces which regulate the vibrations of the aether do 
not vary according to Newton’s law of universal gravitation, but 
that these forces are repulsive, and vary according to an inverse 
power of the distance greater than two. M. Cauchy, in his Me- 
moire sur la Dispersion de la Lumiere,” had inferred from his ana- 
lysis that “ in the neighbourhood of contact, the action of two 
particles is repulsive, and reciprocally proportional to the fourth 
power of the distance.” 
Mr. Kelland, in a memoir contained in the previous volume of 
these Transactions, (vol. vi. Part I. p. 178) had been led by calcu- 
lations founded upon the phsenomena of the dispersion of light, to 
conclude that the particles of the ccther act on each other with 
forces varying inversely as the square of the distance. We shall not 
here pretend to discuss the difterence of the results thus obtained 
by these two mathematicians. But we must notice Professor Kel- 
land’s memoir “ On Molecular Equilibrium,” contained in the vo- 
lume now under our notice. In this notice Mr. Kelland pursues a 
train of speculation somewhat similar to that employed in the last 
century by Dr. Knight, in his “ Attempt to explain all the phoeno- 
mena of Nature by two principles, attraction and rejDulsion and 
by Boscovich, in his “ Theory of Natural Philosophy reduced to a 
single law of the forces which exist in Nature.” Mr. Kelland states 
his assumption as follows : “I purpose to commence my investiga- 
tion by retaining M. Mosotti’s hypothesis of two systems of parti- 
cles*, repulsive towards atoms of their own kind, but each respect- 
ively attractive towards the atoms of the other. We will call one 
system of particles caloric, and the other matter.” He then adds the 
other suppositions by which these two elements are distinguished 
from each other ; the atoms of caloric are distributed through 
space, the atoms of matter occupy only given f)ositions. In both the 
density will vary from point to point ; but the particles of matter 
are supposed to be much more widely separated than the particles 
of caloric ; so that a material particle may be considered as a nu- 
cleus about which the particles of caloric are collected, forming its 
atmosphere. But Mr. Kelland afterwards determines the conditions 
of equilibrium of a system in which the atoms of caloric are re- 
pulsive of those of matter ; and on the same hypothesis he deter- 
mines the mutual action of two particles of matter, together with 
the caloric surrounding them. For the general relations between 
* Taylor’s Scientific Memoirs, vol. i. p. 448, and L. and E. Phil. Mag. 
vol. X. p. 320. 
