'To this Mr. Whewell, in his "Philosophy of the Inductive Sciences," makes the following reply:--"But Bartholinus could have seen no such consequence in the accident, if he had not previously had a clear conception of single refraction. A lady, in describing an optical experiment which had been shown her, said of her teacher, 'he told me to increase and diminish the angle of refraction: and, at last, I found that he only meant me to move my head up and down.' At any rate, till the lady had acquired a knowledge of the meaning which the technical terms convey, she could not have made Bartholinus's discovery by means of this accident. Suppose that Huygens made the experiment alluded to, without design, what he really observed was that the images appeared and disappeared alternately as he turned the rhomb round. His success depended on his clearness of thought, which enabled him to perform the intellectual analysis which would never have occurred to most men, however often they had combined two rhombs in different positions. Malus saw that in some positions the light reflected from the windows of the Louvre became dim. Another person would have attributed this to accident; he, however, considered the position of the prism, and the window; repeated the experiment often; and by virtue of the eminently distinct conceptions of space which he possessed, resolved the phenomenon into its geometrical conditions."* "If it were true, that the fall of an apple was the occasion of Newton's pursuing that train of thought which led to the doctrine of universal gravitation, the habits and constitution of Newton's intellect were the real source of this great event in the progress of knowledge."** "In whatever manner facts may be presented to the notice of a discoverer, they can never become the materials of exact knowledge, except they find his mind already provided with precise and suitable conceptions, by which they may be analysed and connected."'*** * Whewell: Phil. Induct. Sciences, vol. 2. pp. 199-1. ** Ibid, vol. 2, p. 189. *** See J. N. Bailey's Essays pp. 87-8-9. These admissions seem to me to prove that whenever a casual fact proves to us a new truth, it does so by its coincidence with previously known facts, and that the novelty of the occasion attracts all credit to itself, and we lose sight of the generalisation below--the fruitful soil of experience on which the new fact, like a seed, falls. We only recognise difference by comparison, and the comparison is an induction, however slender.