MECHANICS AND PROPERTIES OF MATTER
1. Province of Physics.-As a result of the observations and experiments made during many generations we are led to make certain assumptions or axioms which state that the physical universe has an objective existence, and that we are made acquainted with it solely by means of our senses. If further we give the name thing to that with the objective existence of which we are acquainted by our senses, then it follows that in the physical universe there are only two classes of things; to these the names Matter and Energy are given. Time and space, and many other quantities, such as Number, Velocity, Position, Temperature, &c., are not things.
It will probably be allowed at once that every form of matter, i.e. a stone, a drop of water, the air, &c., has objective existence; the most powerful argument in favour of this belief being the fact that all experiments have shown that under no circumstance whatever can we alter the quantity of matter. This result of experience, which is a fundamental assumption in all quantitative chemical experiments, is generally referred to as the Conservation of Matter.
The statement that energy has an objective existence is, however, one which is not so readily accepted: in fact its acceptance by scientific men only dates back a comparatively short time. Experiments, with which we shall deal later on, have however shown that energy, like matter, is indestructible and uncreatable by man. The objective existence is, as Professor Tait has pointed out, virtually admitted in a curious way by its being advertised for sale, it being quite common in manufacturing centres to see the notice "Spare Power to Let." Again, water under a great