When we also take into account the fact that Aether is gravitative, and therefore denser nearer to the sun than further away, and that it is also rotating round the central body the sun (Art. 91), then we have at once every condition necessary to explain all the various kinds of cometary tails, and also for the remarkable fact that the tail is always turned away from the sun, which is simply due to the effect of the rotating Aether with its outflowing electro-magnetic waves upon the gaseous matter of the comet. Thus from the phenomena of comets' tails, we have again arrived at the conclusion of the existence of that centrifugal force, whose origin and continuity are to be found in the electro-magnetic Aether which surrounds the sun, and which by its electro-magnetic waves gives rise to pressure on all bodies upon which they fall. ART. 116. _Formation of Tails._--With the conception of the formation of the comet advanced in Art. 111, viz. that it is nothing more or less than Aether in a state of condensation, and remembering the explanation given of the parts of the comet, as the nucleus, and head or coma, we are now in a position to give a philosophical account of the formation of the tails of comets, which will satisfactorily fulfil all the Rules of Philosophy. In addition to the facts already referred to in the previous articles of this chapter, we must also recall our conception of the Aether as given in Chapter IV., remembering that it gets denser nearer the sun, and that it is not frictionless; therefore, when a body is urged through it, friction is produced, and heat is generated. We must also remember that the Aether is rotating round the sun as that body proceeds through space. We have, therefore, to picture the condensed mass of Aether situated out in the cold interstellar space, gradually coming under the influence of the sun, as that body rushes on its journey through space with a velocity of 500,000 miles per hour. Slowly, but surely, the mass of condensed Aether begins to respond to the attractive power of the sun, and to move through space towards the sun. So long as it is moving towards the sun, it is encountering and having to overcome the resistance of the Aether. At first this resistance is very feeble, owing to the decreased density of the Aether, but as it proceeds on its journey it is constantly passing into denser parts of the aetherial electro-magnetic field around the sun. The result is, that as the resistance is increased, so there is greater friction between the matter of the comet and the atomic Aether in space, and, in consequence, heat is generated.