40 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
sociated, and their existence, as such, rendered impossible be proved, 
the same reasoning goes to show that the necessity of supposing the’ 
seat of the heat vibrations to lie in the elementary constituents. 
of the molecules would not follow. 
Tyndall in one of his contributions to Molecular Physics argues. 
that since the power of absorption of a vapor depends on that of the 
liquid from which it has been obtained, or since the state of aggre- 
gation does not alter the relative power of absorption of bodies, the 
seat of absorption must lie in the atoms—not in the molecules—the 
relative positions of the molecules being altered, and consequently 
the conditions of molecular motion. To this it may be replied that 
the change in the intermolecular relations involved in a change 
in the state of aggregation of a body does not necessitate any alter- 
ation in the periods of the molecular vibrations but may merely 
lengthen or shorten their amplitudes. 
On the other hand were the atoms the seat of the heat vibrations, 
such undoubted facts as that water has such profoundly different 
physical properties from both hydrogen and oxygen, that ozone has. 
many times the absorbing power of oxygen, and that ammonia has 
about 5000 times the absorbing power of either of its constituents, 
hydrogen or nitrogen, would be utterly incapable of explanation. 
On the whole these considerations, combined with the general law 
that heat for the most part produces physical and not chemical 
effects, though molecular motion may undoubtedly be transtormed. 
into atomic motion subject to the law of the conservation of energy, 
seem to point irresistibly to the conclusion that heat is not only 
a form of energy but more particularly that it consists in molecular 
motions. The relation of heat to light is shown clearly by the 
analysis of light by means of a prism, and lies in the fact that all 
the undulations of the energipherous medium, if transformed into the 
molecular motion of bodies, or if allowed to excite the tactile nerves 
manifest themselves in the form of heat, while only a limited portion: 
when allowed to strike the eye excites the optic nerve and produces. 
the sensation of sight. In a manner which we now propose briefly 
to describe similar, more or less intimate, connexions have been: 
established between heat and the other forces of nature, so that heat, 
light, electricity, magnetism, sound, chemical affinity, potential and 
mechanical energy are now generally regarded as but different forms 
of an unchangeable amount of indestructible energy. 
