Thus we learn from the dynamical action of light, that not only is the sun the centre of an attractive force, but that it is equally the centre of a repellent or repulsive power or motion; which repulsive power always follows the path of the radius vector, and diminishes with an intensity which is inversely as the square of the distance. What we have to ask ourselves therefore is, whether the repulsive power of light is the Centrifugal Force that we are trying to discover? In Art. 24 we found out what were the necessary characteristics of the Centrifugal Force, which is to form the companion law to the attractive law of gravity, or the Centripetal Force. We there saw that this centrifugal law must be universal in character; that it must coincide with the path of the centripetal force; that it must also be subject to the same law of intensity, viz. the law of inverse squares; and further, that the force must be proportional to the product of the two masses concerned. We find in the repulsive power of light three at any rate of these conditions fulfilled. Light is universal because Aether is universal. It is always subject to the law of inverse squares, and what is more, its repelling power coincides exactly with the path which the centripetal force takes, that is, the radius vector. We have not, however, discovered that light fulfils the remaining necessary condition, which is, that the repelling powers of light emitted by any two bodies are equal to the product of their masses. So that until this is done, it cannot be said that the aetherial light waves form the centrifugal force or motion from a central body that we are seeking for. But while that may be true, yet if light be not the centrifugal motion, it certainly indicates in what direction we are to look for that force, and that is to the Aether, whose periodic waves give rise to the phenomena of light. For, after all, light is due to aetherial wave motion, and, therefore, while light from certain standpoints may be conceived to be the cause of other phenomena, yet primarily the real cause of all phenomena which are due to light are due to the aetherial waves which themselves give rise to the phenomena of light. Thus light acts as a guide-post to us, pointing out the direction we should take in order to find out the real centrifugal force or motion, and as plainly as it possibly can, it indicates to us that the true solution of our centrifugal motion that we are seeking for is to be found, and alone found, in that universal aetherial medium which, by its vibrations and wave motions, gives rise to that which we term Light. In conclusion of this point, it may be pointed out that Professor Challis[20] also took this view of light, as he distinctly states that "Light is to be ranked with the physical forces, and its dynamical action is equally to be ascribed to the pressure of the Aether," and then proceeded to show how repulsion could be exerted on atoms by the periodic wave motion of the