342 A SHORT HISTORY OF SCIENCE 



of Newton the perturbations of the planets had been the subject 

 of continual observation and study. Improved telescopes de- 

 manded - - and at the same time facilitated - - more extended 

 and refined computations. Discrepancies between computed and 

 observed positions indicated disturbing forces of known or in some 

 cases unknown origin. In particular, irregularities never ex- 

 ceeding two minutes of arc - - in the motion of the most recently 

 discovered planet Uranus, led the young Cambridge graduate 

 John Couch Adams (1819-1892) and the eminent French astrono- 

 mer Leverrier (1811-1877) to independent attacks on the for- 

 midable problem of determining the mass and position of a 

 hypothetical new planet which could cause the observed effects 

 on Uranus. Unfortunately for Adams the necessary cooperation 

 on the part of the observatories was not promptly available, so 

 that the actual discovery connected itself with the somewhat 

 later work of Leverrier. The discovery was naturally accepted 

 as an extraordinary illustration of the power of mathematical as- 

 tronomy and a convincing proof of the Newtonian theory of 

 gravitation. 



The discovery of this planet [Neptune] is justly reckoned as 

 the greatest triumph of mathematical astronomy. Uranus failed 

 to move precisely in the path which the computers predicted for it, 

 and was misguided by some unknown influence to an extent which 

 a keen eye might almost see without telescopic aid. . . . These 

 minute discrepancies constituted the data which were found sufficient 

 for calculating the position of a hitherto unknown planet, and bring- 

 ing it to light. Leverrier wrote to Galle, in substance : Direct your 

 telescope to a point on the ecliptic in the constellation of Aquarius, in 

 longitude 326, and you will find within a degree of that place a new 

 planet, looking like a star of about the ninth magnitude, and having a 

 perceptible disc. The planet was found at Berlin on the night of 

 Sept. 26, 1846, in exact accordance with this prediction, within half 

 an hour after the astronomers began looking for it, and only about 

 52' distant from the precise point that Leverrier had indicated. 



Young. 



While the telescope serves as a means of penetrating space, and 

 of bringing its remotest regions nearer us, mathematics, by inductive 



