Taking these two, Matter and Energy, as distinct, let us concentrate for a little upon each of them separately. Let us first turn attention upon MATTER. This form of existence is most easily contemplated, as most directly presenting itself to observation. A piece of metal may best serve for illustration, such as the _iron_ out of which we form so many of our industrial implements. This metal may be mingled through earth or rock; it may be held in solution in water, or made to flow out in liquid form from the furnace; it may be hardened either in the more brittle form of cast iron, or in the more rigid form known as malleable; but through all these changes the material is the same. Further, suppose we were to receive a quantity of ore, and for the sake of experiment were to have part presented in each one of these forms, the quantity would continue exactly the same as was originally received. To quote again from the same author:--"The grand test of the reality of what we call Matter, the proof that it has an objective existence, is its indestructibility and uncreatability--if the term may be used--by any process at the command of man. The value of this test to modern chemistry can scarcely be estimated. In fact we can barely believe that there could have existed an exact science of chemistry had it not been for the early recognition of this property of matter; nor in fact would there be the possibility of a chemical analysis, supposing that we had not the assurance by enormously extended series of previous experiments, that no portion of matter, however small, goes out of existence, or comes into existence in any operation whatever. If the chemist were not certain that at the end of his operations, provided he has taken care to admit nothing and to let nothing escape, the contents of his vessels must be precisely the same in quantity as at the beginning of the experiment, there could be no such thing as chemical analysis."[AF]