SIXTH ORDINARY MEETING. 37 
conceptual elements of motion, and as such has been justly denomi- 
nated the ‘“ great independent variable,” yet to the physicist it cannot 
be regarded as by any means an elementary idea. This will be 
apparent if we remember the conventional measure of time univers- 
ally employed. That measure shows that time is recognised, not as 
a primordial idea, but as a very complex conception involving motion, 
position and space. 
Further, it seems utterly inconsistent with what is now known of 
_ the nature of force, to regard it as an elementary idea. If matter be 
really inert, the only rational use of the word force is to denote 
certain mechanical facts of motion. We may therefore for our present 
purposes regard space, matter, position and motion as the only 
elementary ideas in the physical world. 
Heat consequently must be referred to these ideas or to combina- 
tions of them. 
The experiments of Davy and Rumford demonstrated that heat 
cannot be matter, since they were able to extract an unlimited amount 
of heat from a limited quantity of matter, thus proving that the 
production of heat did not involve the consumption of matter. These 
experiments, together with an innumerable number of others of 
similar nature, show that the essential idea of heat lies in motion. 
But since to have motion matter must move, it is more correct to 
define Heat as a fori of Energy than of Motion. From the fact 
that there is a mechanical equivalent of heat, it follows that the 
quantity of heat is proportional not to the quantity of motion, but 
to the quantity of energy. Thus Tyndall’s brilliant work ‘“ Heat as a 
Mode of Motion,” would have been more correctly and appropriately 
entitled, ‘“‘ Heat as a Form of Energy.” Besides being more correct, 
this designation would have the important advantage of suggesting 
the remarkable connection of heat with light, magnetism, electricity, 
&e., by virtue of the Conservation of Energy, a principle, the 
discovery of which is perhaps the grandest reward of the scientific 
research of modern times. 
Having then established that heat is a form of energy, it becomes 
necessary to consider the question—Are there two essentially different 
kinds of energy, kinetic and potential? If potential energy be 
defined (as it generally is) to be the energy of position, its existence 
is utterly inconsistent with the proposition that matter is inert, a pro- 
position the truth of which lies at the foundation of Modern Physics. 
