Again: "The colours of bodies arise from the magnitude of the particles that reflect them. Now, if we conceive these particles of bodies to be so disposed among themselves, that the intervals, or empty spaces between them, may be equal in magnitude to them all; and that these particles may be composed of other particles much smaller, which have as much empty space between them as equals all the magnitudes of these smaller particles; and that in like manner these smaller particles are again composed of others much smaller, all which together are equal to all the pores, or empty spaces, between them; and so on perpetually till you come to solid particles, such as have no pores, or empty spaces within them: and if in any gross body there be, for instance, three such degrees of particles, the least of which are solid; this body will have seven times more pores than solid parts. But if there be four such degrees of particles, the least of which are solid, the body will have fifteen times more pores than solid parts. If there be five degrees, the body will have one and thirty times more pores than solid parts. If six degrees, the body will have sixty and three times more pores than solid parts. And so on perpetually(44)." (44) Ibid. In the Queries annexed to the Optics, Newton further suggests an opinion, that the rays of light are repelled by bodies without immediate contact. He observes that: "Where attraction ceases, there a repulsive virtue ought to succeed. And that there is such a virtue, seems to follow from the reflexions and inflexions of the rays of light. For the rays are repelled by bodies, in both these cases, without the immediate contact of the reflecting or inflecting body. It seems also to follow from the emission of light; the ray, so soon as it is shaken off from a shining body by the vibrating motion of the parts of the body, and gets beyond the reach of attraction, being driven away with exceeding great velocity. For that force, which is sufficient to turn it back in reflexion, may be sufficient to emit it. It seems also to follow from the production of air and vapour: the particles, when they are shaken off from bodies by heat or fermentation, so soon as they are beyond the reach of the attraction of the body, receding from it and also from one another, with great strength; and keeping at a distance, so as sometimes to take up a million of times more space than they did before, in the form of a dense body."