32 ROUGH WAYS MADE SMOOTH. 



NEW PLANETS NEAR THE SUN. 



PERHAPS no scientific achievement during the present cen- 

 tury has been deemed more marvellous than the discovery of 

 the outermost member (so far as is known) of the sun's 

 family of planets. In many respects, apart from the great 

 difficulty of the mathematical problem involved, the discovery 

 appealed strongly to the imagination. A planet seventeen 

 hundred millions of miles from the sun had been discovered 

 in March, 1781, by a mere accident, though the accident 

 was not one likely to occur to any one but an astronomer 

 constantly studying the star-depths. Engaged in such ob- 

 servation, but with no idea of enlarging the known domain 

 ofthesun > Sir W. Herschel perceived the distant planet 

 Uranus. His experienced eye at once recognised the fact 

 that the stranger was not a fixed star. He judged it to be a 

 comet. It was not until several weeks had elapsed that the 

 newly discovered body was proved to be a planet, travelling 

 nearly twice as far away from the sun as Saturn, the re- 

 motest planet before known. A century only had elapsed 

 since the theory of gravitation had been established. Yet it 

 was at once perceived how greatly this theory had increased 

 the power of the astronomer to deal with planetary motions. 

 Before a year had passed more was known about the motions 

 of Uranus than had been learned about the motion of any 

 of the old planets during the two thousand years preceding 

 the time of Copernicus. It was possible to calculate in 

 advance the position of the newly discovered planet, to 



