476 
ON T1IE TRIPLET OF TERMS, 
be going on ; increase the rapidity of the vibration, and you get what is called 
increase of temperature—the body becomes hotter ; diminish the rapidity, and 
you get depression of temperature, or cooling. Allow these vibrations to as¬ 
sume a rhythmical order, to take the form of waves, and the propagation of 
heat by radiation is accounted for. 
It was at a period still less remote, no more than about forty years 
ago, that the old “ emission theory ” of light came to be displaced from 
the convictions of philosophers. It had been held since the time of Sir 
Isaac Newton that there existed minute particles of excessive tenuity, 
which, darting out from luminous bodies through space and through 
transparent media at the rate of something like 160,000 miles a second, 
gave rise to the phenomena of light. But in consequence ot certain phe¬ 
nomena being discovered, the existence of which could not be explained b}^ 
the aid of this theory of corpuscles, attention was drawn more forcibly to the 
“ theory of undulation,” which then almost at once supplanted it, and has 
held its ground since. Belief is now fixed, not in the existence of rapid- 
shooting particles, but in waves formed by the rhythmical vibrations of an 
ether which is supposed to exist throughout space. Whisperings have not been 
wanting that this “ ether” may somehow be connected with ordinary matter, 
either as the materiel prim a, out of which all things were in the beginning 
educed, or perhaps, as the ruins into which the clumsy molecules of gravita¬ 
ting matter may have tumbled. That there is something possessing inertia 
diffused through the interplanetary spaces seems likely from the fact known 
to astronomers that the motion of certain comets is continually diminishing. 
In the early days of the science of electricity, all the phenomena manifested 
by this wondrous agent were ascribed to the existence of a fluid; afterwards 
the hypothesis of two fluids was required. The existence of fluids in elec¬ 
trically excited bodies has, however, been for some time regarded as a myth. 
From the fact that electricity and magnetism are mutually convertible, and 
these again producible from, and reducible to, heat, light, or ordinary motion; 
and taking into account the circumstance that they are unknown apart from 
ordinary matter, it has been conjectured that these ‘'fluids may in reality 
be a motion of a peculiar kind existing in the particles of bodies. Heat, light, 
electricity, and magnetism are then motion. 
By an extension of the idea, superposed upon a revival of the long-cherished 
notion of the universality and unity of origin of matter, “ it is conceivable 
that the various kinds of matter now recognized as different elementary sub¬ 
stances, may possess one and the same ultimate or atomic molecule, existing 
in different conditions of movement.” # These are the words of a philosopher, 
unhappily for science, now no more ; and they were written at the conclusion 
of a life which had been devoted to the study of molecular dynamics. If ve 
accept them, we arrive at a generalization as grand as it is simple in concep¬ 
tion, as universal as it is obedient to the requirements of science. _ 
The phenomena of which we are the witnesses, and which in our own 
bodies we serve to exemplify, are continually reminding us that all in the 
universe is change. Change, we may henceforth believe, is motion. 
ON THE TRIPLET OF TERMS—MATTER, SUBSTANCE, BODY. 
BY A PROVINCIAL ATOM. 
In offering some remarks upon the three appellatives which stand at the head 
of this paper, I have no intention either of covering the same ground t hat is tra- 
* Graham: “Speculative Ideas respecting the Constitution of Matter, Journ. Chem. Soc. 
vol. xvii. p. 368. 
