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 idsa. 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 form 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,, 

 &c, 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 1 Tf 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. 



