12 JOURNAL OF THE 
this hypothesis of the essential unity of matter with the 
equal action of gravity upon all bodies. He recognizes that 
the numerous and varying properties of the solid and liquid, 
no less than the few grand and simple features of the gas, 
may all be dependent upon atomic and molecular mobility. 
Let us imagine, he says, one kind of substance only to exist 
—ponderable matter; and, further, that matter is divisible 
into ultimate atoms, uniform in size and weight. We shall 
have one substance and a common atom. With the atom at 
rest the uniformity of matter would be perfect. But the 
atom possesses always more or less motion, due, it must be 
assumed, to a primordial impulse. ‘This motion gives rise to 
volume. The more rapid the movement, the greater the 
space occupied by the atom, somewhat as the orbit of a plan- 
et widens with the degree of projectile velocity. Matter is 
thus made to differ only in being lighter or denser matter. 
The specific motion of an atom being inalienable, light mat- 
ter is no longer convertible into heavy matter. In short, 
matter of different density forms different substances—differ- 
ent inconvertible elements, as they have been considered.” 
The hypothesis that the elements are built up of two or 
more common constituents has a larger number of supporters 
and would seem more plausible. Some have supposed one 
such primal element by the condensation or polymerization of 
which the others were formed. Thus we have the hydrogen 
theory of Prout, modified to the one-half atom by Dumas, and 
finally by Zangerle to the one-thousandth hydrogen atom. 
The suggestion of Crookes as to the genesis of the elements 
from the hypothetical pvoty/e, under the influence of electrici- 
ty, may also be mentioned here. 
Others have adopted the supposition of two elements, Rey- 
nolds making one of these an element with a negative atomic 
weight, whatever that may mean. Low and others have 
fixed upon carbon and hydrogen as the two elements. 
There are many practical difficulties in the way of these 
suppositions ; the lack of uniformity in the differences be- 
tween the atomic weights, the sudden change of electro-chem- 
ical character, and the impossibility, so far, of discovering 
