That the particles of light, like those of heat, are endowed with a repulsive force which prevents them from accumulating when in a state of condensation, or when they are detained by the absorptive action of opaque bodies, will be readily admitted. By this power a beam of light radiating from a luminous point has, in every azimuth, the same degree of intensity at the same distance from its centre of divergence; but if we intercept a portion of such a beam by an opaque body, the repulsive force of the light which formerly occupied its shadow is withdrawn, and consequently the rays which pass near the body will be repelled into the shadow, and will form, by their interference with those similarly repelled on the other side, the interior fringes, which are parallel to the edges of the body. The rays which pass at a greater distance will in like manner be bent towards the body, but with less force, and, interfering with those rays which retain their primitive direction, from the state of their fits or the position of their poles, they will form the exterior fringes. When the inflecting body is placed near the point of divergence, the greater proximity of the rays will produce a greater repulsive force, and consequently a greater inflection of the passing light; while the removal of the body from the point of divergence will be accompanied with an increased distance of the particles, an inferior repulsive force, and a feebler inflection. As the phenomena of inflection, considered under this aspect, arise from a property of the light itself, it follows that they will remain invariable, whatever be the nature or density of the body, or the form of the edge which acts upon the passing rays. CHAPTER IX. _Miscellaneous Optical Researches of Newton—His Experiments on Refraction—His Conjecture respecting the Inflammability of the Diamond—His Law of Double Refraction—His Observations on the Polarization of Light—Newton’s Theory of Light—His “Optics.”_ Before concluding our account of Newton’s optical discoveries, it is necessary to notice some of his minor researches, which, though of inferior importance in the science of light, have either exercised an influence over the progress of discovery, or been associated with the history of other branches of knowledge.