620 THE POPULAR SCIENCE MONTHLY, 



tween theory and observation in so accurate a science as astronomy 

 could not be overlooked. Long before this, the hypothesis had been 

 advanced that the deviations were caused by the attractive force of 

 an unseen and still more distant planet ; but, as no such planet had 

 been discovered, the hypothesis had remained until now wholly bar- 

 ren. The hypethesis, however, was reasonable, and furnished the 

 only conceivable explanation of the facts ; and, moreover, if true, the 

 received system of astronomy ought to be able to assign the position 

 and magnitude of the disturbing body, the magnitude and direction 

 of the displacements being given. 



This possibility was generally appreciated by astronomers, and the 

 very great length and difficulty of the mathematical calculation which 

 the investigation involved was probably the reason that no one had 

 hitherto undertaken it. Le Yerrier, however, had both the courage 

 and the youthful strength required for the work. And now the great 

 work had been done; and, on the 18th of September, Le Yerrier had 

 sent to the Observatory of Berlin his communication announcing the 

 final result, namely, that the planet would be found about 5° to the 

 east of the star Delta of Capricorn. 



The letter containing this announcement was received by Galle, at 

 Berlin, on the 23 d, and it was Galle whom we left measuring the po- 

 sition of that faint star on the evening of the 24th. It so happened 

 that a chart of that portion of the heavens had recently been prepared 

 by the Berlin Observatory, and was on the eve of publication ; and, 

 on the very evening he received the letter, Galle had found, near the 

 position assigned by Le Yerrier, a faint star, which was not marked 

 on this chart. The object differed in appearance from the surround- 

 ing stars, but still it was perfectly possible that it might be a fixed 

 star which had escaped previous observation. 



But, if a fixed star, its position in the constellation would not vary, 

 while, if a planet, a single night would show a perceptible change of 

 place. Hence, you may conceive of the interest with which Galle 

 was measuring anew its position on the evening of the 24th. 



The star had moved, and in the direction which theory indicated ; 

 and for once, at least, the world rang with applause at a brilliant 

 scientific conquest, from which there was not one cent of money to be 

 made. Yet, was that conquest any the less important to the world ? 

 What had it secured? It had confirmed the theory of astronomy 

 which Copernicus and his successors had built up, and it had clinched 

 the last nail in the proof that those grand conceptions of modern 

 astronomy, now household thoughts, are realities, and not dreams. 

 Certainly no military conquest can compare with this. 



Do you smile at the enthusiasm wliich rates so high a purely intel- 

 lectual achievement ? Go out with me under the heavens, in some star- 

 lit night, and, looking up into the depths of space, recall the truths 

 you have learned in regard to that immensity, and allow the imagina- 



