doctrine that light is a material substance. Now Newton had, as a matter of fact, a great dislike of the more imaginative kind of hypotheses; he altogether renounced the attempt to construct the universe from its foundations after the fashion of Descartes, and aspired to nothing more than a formulation of the laws which directly govern the actual phenomena. His theory of gravitation, for example, is strictly an expression of the results of observation, and involves no hypothesis as to the cause of the attraction which subsists between ponderable bodies; and his own desire in regard to optics was to present a theory free from speculation as to the hidden mechanism of light. Accordingly, in reply to Hooke's criticism, he protested[1] that his views on colour were in no way bound up with any particular conception of the ultimate nature of optical processes.
Newton was, however, unable to carry out his plan of connecting together the phenomena of light into a coherent and reasoned whole without having recourse to hypotheses. The hypothesis of Hooke, that light consists in vibrations of an aether, he rejected for reasons which at that time were perfectly cogent, and which indeed were not successfully refuted for over a century. One of these was the incompetence of the wave-theory to account for the rectilinear propagation of light, and another was its inability to embrace the facts--discovered, as we shall presently see, by Huygens, and first interpreted correctly by Newton himself-of polarization. On the whole, he seems to have favoured a scheme of which the following may be taken as a summary[2]:—
All space is permeated by an elastic medium or aether, which is capable of propagating vibrations in the same way as the
- ↑ Phil. Trans. vi, 1672, p. 5086.
- ↑ Cf. Newton's memoir in Phil. Trans. vii, 1672; his memoir presented to the Royal Society in December, 1675, which is printed in Birch, iii, p. 247; his Opticks, especially Queries 18, 19, 20, 21, 23, 29; the Scholium at the end of the Principia; and a letter to Boyle, written in February, 1678-9, which is printed in Horsley's Nextoni Opera, p. 385.
In the Principia, Book I., section xiv, the analogy between rays of light and streams of corpuscles is indicated; but Newton does not commit himself to any theory of light based on this.
C
