For example, let us take an iron ball, and apply heat to it, either by putting it in a furnace or suspending it in some way over an intense heat. As the heat, which is vibratory motion of the Aether, begins to be absorbed by the iron ball, it sets the atoms which compose the ball in motion, urging them to separate, and thus cause the iron ball to expand and increase in volume. As greater heat is absorbed, so greater motion among the atoms is the result. So that the motion of heat is tending all the time to expand the body, while they are held together by the attraction of cohesion, whatever that may be. As the heat is further increased, the iron ball begins to assume a liquid or molten form, its atoms beginning to move about with greater freedom, though held together by a decreased attractive power. In this condition we now say that it is in the molten state. Now during all this time, what has the Aether been doing, or what part has it played in the expansion and changing of the solid to a liquid? We have to remember, from Art. 60, that wherever there is motion of any kind or sort, there we have a capacity to do work, and that the aetherial motion which we term heat is no exception to this rule. We are now no longer dealing with a frictionless medium, but with a medium which possesses weight, because it is gravitative, and consequently possesses inertia also. So that whenever the Aether is set in motion by flame or heat, its motion would be transmitted by waves of some kind to the iron ball. These periodic waves, acting upon the mass of the ball, attack the molecules of the ball and begin to set them in motion. It is supposed that they are already in motion, as nothing is absolutely cold, and the motion of the aetherial waves imparts a greater motion still to the molecules, with the result that the agitation becomes greater and greater, until at length the agitation becomes so great, that the molecules break away from the power of attraction that holds them together, and so begin to move about with greater freedom and with greater rapidity. It is this state which we call molten. Now if Aether be frictionless, as has hitherto been supposed, and if heat be due to the vibratory motions of Aether, the problem confronts us, as to how the motion of a frictionless medium can do work in expanding a body, and urging the molecules of a body further and further apart. If the Aether be frictionless, then the waves of Aether known as aetherial heat waves ought to pass between the atoms as water passes through a sieve, or wind passes through a forest. Yet it is assumed that the vibratory motions of a hot body are caused by vibrations of the periodic waves of the Aether, which act upon the molecules of the body; and, in order for such an assumption to be consistent with the results, the only possible conception that can be accepted of the Aether, is that it is gravitative, and consequently possesses mass and inertia, and therefore