Looking at the subject from the standpoint of the solar system, with the sun as the central body, we see that while we have the sun, which acts as the controlling centre of the particular system of planets, holding all the planets in their orbits by its attractive power, yet at the same time it is also the source of all light and heat. Now heat being due to the wave motion of the aetherial medium, such motion being always exerted from the central body, we arrive at the only legitimate conclusion that can be arrived at, viz. that the sun is also the source of a repulsive motion, which motion coincides with the path that the attractive power of Gravitation takes, that is, along the radius vector of the circle, as shown in Art. 20. ART. 66. _Law of Inverse Squares applied to Heat._--The law of inverse squares which governs not only the Law of Gravitation Attraction (Art. 22), but also electricity and light, is equally applicable to the phenomena of heat, so that we say the intensity of heat varies inversely as the square of the distance. Thus, if we double the distance of any body from the source of heat, the amount of heat which such a body receives at the increased distance is one-quarter of the heat compared with its original position. If the distance were trebled, then the intensity of the heat would be reduced to one-ninth; while if the distance were four times as great, the intensity of the heat would only be one-sixteenth of what it would receive in its first position. This may be proved from experiments as given by Tyndall in his _Heat, a Mode of Motion_.