SEARCHING FOR ONE THING AND FINDING ANOTHER. 517 



observed with comparative exactness), to the exclusion of 

 their distances (which cannot be measured with much 

 correctness), and by inventing a method which depended 

 upon the whole body of observations, and not upon 

 selected ones only, for the determination of the motion, 

 has made his investigations by far the most satisfactory 

 of those which have appeared. The result is that it has 

 been rendered very probable that in several of the double 

 stars the two stars describe ellipses about each other ; and 

 therefore that here also, at an immeasurable distance from 

 our system, the law of attraction, according to the inverse 

 square of the distance, prevails. And, according to the 

 practice of astronomers, when a law has been established 

 tables have been calculated for the future motions ; and 

 we have ephemerides of the revolutions of suns round 

 each other in a region so remote that the whole circle of 

 our earth's orbit, if placed there, would be imperceptible 

 by our strongest telescopes.' 1 



So again, { when Newton produced a bright spot on the 

 wall of his chamber, by admitting the sun's light through 

 a small hole in the window-shutter, and making it pass 

 through a prism, he expected the image to be round ; 

 which, of course, it would have been, if the colours had 

 been produced by an equal dispersion in all directions ; 

 but, to his surprise, he saw the image, or spectrum, five 

 times as long as it was broad. He found that no con- 

 sideration of the different thickness of the glass, the pos- 

 sible unevenness of its surface, or the different angles of 

 rays proceeding from the two sides of the sun, could be 

 the cause of this shape. He found, also, that the rays did 

 not go from the prism to the image in curves ; he was 

 then convinced that the different colours were refracted 

 separately, and at different angles ; and he confirmed this 

 1 Whewell, History of Inductive Philosophy, vol. ii. 3rd edit. p. 203. 



