Note 94 — Chapter III

All theories of light require these immense numbers. Sir J. Herschel says there is no "mode of conceiving the subject which does not call upon us to admit the exertion of mechanical forces which may well be termed infinite." The numeration in the text is a rough and ready shape of statement at once intelligible. But it is interesting to view the subject more exactly.—Light travels in one second 192,000 miles. Each mile contains 63,360 inches, and in each inch are 39,000 waves of red light, calculated at their mean length. Now, multiply these three sets of figures together, and we get a rate of 474,439,680,000,000 red waves per second. The mean length of a violet wave is the 1/57500th part of an inch; and by a like multiplication we find a product of 699,494,400,000,000 of violet light-strokes thrown upon the retina in each second. The phrase "millions of millions" is used in the text, because few people realize the idea of any arithmetical whole beyond a million.