The capacity of bodies to radiate and to absorb differ considerably. Dr. Franklin made several simple experiments to prove the relative powers of radiation and absorption with several pieces of cloth. These were put out on the snow, and exposed to the heat of the sun. He found that the pieces which were dark in colour sank deepest into the snow, while those which were lightest in colour sank the least. From this he inferred that the darkest pieces were the best absorbers, and therefore the best radiators, while the light-coloured cloths were the worst absorbers, and therefore the worst radiators. Radiation, therefore, may be said to be the propagation of a wave motion through the Aether; and, as all motion is a source of power or energy, we have in the radiation of heat from one body to another by the aetherial waves, the transmission of a motive power capable of doing work, either internal work as increasing the temperature of the molecule or body, or external work as separating the atoms, or driving them further apart. It can readily be seen that if the Aether were frictionless, as has generally been supposed, the Aether could not have any motive power at all, and therefore could not transmit heat from one body to another. Professor Tyndall[10] on this point says, referring to the cooling of a red-hot ball: "The atoms of the ball oscillate in a resisting medium, which accepts their motion and transmits it on all sides with inconceivable velocity." Now in the previous quotation given in this article from the same authority, he states that the atoms are immersed in the Aether. So that evidently in his opinion the Aether and the resisting medium are one and the same. So that our assumption of the gravitative property of the Aether is perfectly in accord with Professor Tyndall's conception of the Aether, in so far as it concerns the propagation of heat waves; and, as will be shown later on, heat and light waves are due to the same physical agent--that is, the Aether; therefore, wherever we get heat and light, there, according to Professor Tyndall's statement, we must have a resisting medium, and as Aether fills all space, the resisting medium must fill all space. This is perfectly in accord with our assumption that the Aether is gravitative and possesses inertia--that is, the capacity to receive and to impart motion, and being gravitative it possesses mass or weight, which is the very quality necessary for the existence of a resisting medium. [Footnote 9: _Heat, a Mode of Motion._] [Footnote 10: _Heat, a Mode of Motion._] ART. 63. _Heat is a Repulsive Motion._--Whatever be the particular character of the vibratory motion of the Aether termed heat, there is one fact regarding the same that is very patent and obvious to all; and that is, that the vibratory motion of heat is essentially a repulsive motion, or a motion from a centre and not one to a centre.