as definite in their operation as those that govern the planets in their journeys round the sun. The physicist, however, deals with another and more subtile class of movements in an Ether, which he supposes to pervade space. Waves, strains, pressures, whirls in the ether, account to men of science for many of the facts of heat, light, and electricity. Thus, according to the scientific conceptions of the present day, we have to imagine all the matter in the universe as in a state of movement, some movements large and occurring in vast stretches of space, and others almost inconceivably minute. Nothing in this vast mechanism has come to rest. Each particle of matter is quivering, molecules of all gases are vibrating to and fro, and millions of wavelets are streaming through the ether in all conceivable directions. If we suppose that the essence of life is movement, does not this give one a conception that in a sense the universe is alive?
We have to deal, however, in these lectures with the movements occurring in living matter. We all know that the living things with which we are familiar move. They move their bodies
