234 Notices of Books. (April, 
energies is given (pp. 78-82), and this is immediately followed 
by the ‘‘ Law of Conservation.”. This law asserts that the sum 
of all the various energies of the universe is aconstant quantity, 
or as Prof. Stewart puts it— 
(A) + (B) + (C) + (D) + (E) +(F) + (G) +(H) =a constant quantity. 
Not that any single one energy is constant in itself, for they are 
perpetually changing into each other, but that the sum of these 
variable quantities is a constant quantity. The fourth chapter is 
entirely devoted to an account of the transmutations of energy, 
and the fifth gives the history of the idea from the earliest times, 
and then discusses at some length the dissipation of energy. 
In discussing the early atomic theories, Professor Stewart has 
omitted the claims of Kanada, a Hindu philosopher, whose 
atomic theory was not only more complete and philosophical than 
that of Leukippos and Demokritos, but was also much earlier. 
A very interesting account of this theory (too little known in 
this country) is given by Sir John Colebrooke in his admirable 
articles on the Philosophy of the Hindus (in the ‘‘ Proceedings of 
the Asiatic Society”). The statement that Demokritos ‘‘ was the 
originator of the doctrine of atoms”’ is also incorrect, even as 
regards Greek philosophy, because Demokritos took the idea, 
which he indeed extended, from Leukippos. Again, the idea of 
the ethereal medium pervading all space was originated by the 
Hindus long before the time of Aristotle, and we protest against 
the assertion that Aristotle “caught a glimpse of the idea of a 
medium,” when we find his constant mention of the AiOjp 
and remember that he introduced the very name for it which we 
now adopt. We claim for the ancients much more than our 
author is disposed to grant them: surely they possessed a very 
definite atomic theory, a fairly definite idea of an ethereal 
medium pervading space, an exact idea of the transformation of 
one kind of matter into another, through the intervention of some 
external principle of motion; and at an earlier date than all, a 
four-element theory, which we accept in a too literal sense, but 
which was philosophical and profound for those unexperimental 
ages. Professor Stewart next passes on to ‘“ Descartes, Newton, 
and Huyghens on a Medium.” ‘In modern times, he writes 
Descartes, author of the vertical hypothesis . . . ” (vertical 
should surely read vortical), but Anaxagoras of Klazomene 
conferred upon his v,ovs, which is essentially a mover of 
matter, the property of inducing the vortical motion of atoms; 
and of all modern philosophers, to our mind, Descartes has most 
drawn upon the ideas of the ancients in his Cosmogony. ‘The 
historical portion of this chapter is very slight and insufficient in 
our opinion, but no doubt a longer historical survey would have 
occupied space required for other matters. 
The theory of the dissipation of energy is indeed a startling 
one; we are perpetually converting work into heat, but it is 
impossible to reconvert all the heat produced into work again. 
o- 
