LEVERRIER AND HIS WORK. 4y& 



disturbance by some unknown body. He was in the position, to borrow 

 Prof, Proctor's illustration, of an observer who, traveling (say) along a canal, 

 should observe "that certain waves, which had long been of a particular 

 size, began to grow larger. Suppose that, struck by this, he instituted a 

 careful series of measurements of their size, and at last satisfied himself that 

 they had increased, . . If, however, while he had satisfied himself by his 

 wave measurement that the waves had really increased in size, he had also 

 satisfied himself that during his observations the increase had reached its 

 fall extent, and had even begun to give place to a slow decrease, tending to 

 restore the original size of the waves, he would manifestly have here an in- 

 dication which might serve to tell him of the very spot where the disturb- 

 ance had taken place." Something of this kind had happened in the case 

 of JSTeptune ; and when Leverrier's analysis of the motion of Uranus was. 

 finished, it was seen that the displacement had reached its maximum and 

 was beginning slowly to decrease. In order to produce these percej)tible 

 effects — and many years were occupied in their production, for it is now 

 known that Uranus only completes his circuit in 84 years, while Neptune 

 requires 164 years — Leverrier assumed that another planet must exist; and 

 from the obsei-ved perturbations of Uranus, he calculated the orbit and posi- 

 tion of the unknown world. On the 1st. of January, 1847, six months after 

 Leverrier had completed the calculations, the planet was found within two 

 degrees of where Leverrier j)redicted it would, appear on that date. 



We pass over the long discussion among astronomers as to whether 

 Leverrier or the English obseryer Adams was the true discoverer of JN'ep- 

 tune; both overcame enormous mathematical difficulties, but Avhether 

 Adams first conceived the existence of JSTeptune or not, Leverrier certainly 

 earliest made known the discovery to the world. 



The quite recent discovery of an inter-Mercurial planet, which after- 

 wards proved to be a sun-spot, brought M, Leverrier's investigations into 

 the motions of Mercury prominently forward. He long ago determined that 

 the movements of Mercury as observed, did not accord with those calculated. 

 "The result," he says, "naturally filled us with inquietude. , . Long- 

 years passed, and it was only in 1859 that we succeeded in unraveling the 

 cause of the peculiarities recognized." There exists, he states, in the neigh- 

 borhood of Mercury, doubtless between the planet and the sun. some matter 

 as yet undiscovered; but whether it consists of one or more small planets 

 or other minute asteroids, or even of cosmical dust, he does not positively 

 assert. The present opinion is that the meteoric and cometic matter exist- 

 ing in the sun's neighborhood in enormous quantities, produces the pertur- 

 bations of Mercury; but Leverrier clung to the belief in "Vulcan, and 

 manifested the most intense interest in every alleged discovery of that 

 planet. When Lescerbault believed that he had found the inter-Mercurial 

 world, Leverrier was one of the first to abruptly present himself and to 

 demand how the discoverer had dared "to commit the grave offence of keep- 

 ing your observation secret for nine months. I warn you," he continued.. 



