xx BIOGRAPHICAL NOTICE. 



Academy his third paper on the motion of Uranus, in which he gave the following 

 elements of the disturbing planet : 



Semi-axis Major ............ 36164 or 7 = 0'53l 



Periodic Time ......... 217'387 



Eccentricity ...... 0-10761 



Longitude of Perihelion ... 284 45 



Mean Longitude, 1st January, 1847 ... ... 318 47' 



Mass ............... = ^ = 0-0001075 



True Heliocentric Longitude, 1st January, 1847 ...... 326'' 32' 



Distance from the Sun ... ... 33'OG 



and also comparisons between theory and observation. The paper also contained a detailed 

 investigation, the object of which was to restrict as far as possible the limits within 

 which the planet should be sought. Le Verricr concluded that it would have a visible 

 disc and sufficient light to make it conspicuous in ordinary telescopes. The number of 

 the Comptes Rendus containing this paper could not reach this country until the third 

 or fourth week in September. Le Verrier communicated his principal conclusions to 

 Dr Galle, of the Berlin Observatory, in a letter which was received by him on Sep- 

 tember 23, 1846. The same evening Dr Galle examined the heavens, comparing the 

 stars with Bremiker's map (Hora XXI of the Berlin Academy's star maps). He soon 

 found a star of about the eighth magnitude, nearly in the place pointed out by Le Verrier, 

 which did not exist on the map. There could be little doubt that this was the new 

 planet, and the observations made on the following day showed that its motion was 

 nearly the same as that of the predicted planet. The discovery of the planet was due, 

 not to its disc, but to its absence as a star on Bremiker's map. The existence of this 

 map, which had been but lately published, was unknown to the English astronomers. 

 On October 1 Challis heard of the discovery of the planet at Berlin. He then found 

 that he had actually observed it on August 4 and August 12, the third and fourth 

 nights of his search, so that if the observations had been compared with each other as 

 the work proceeded, the planet might have been discovered by him before the middle 

 of August. When the search was discontinued, on October 1, Challis had recorded 3150 

 positions of stars and was making preparations for mapping them 1 . 



Adams's researches, therefore, preceded Le Verrier's by a considerable interval ; and, 

 in spite of the delay in commencing the search, it had been carried on at Cambridge 



1 Even as it was, the planet was nearly discovered by of July 30 included all those of August 12. After the 



the middle of August. Challis used two methods of discovery of the planet, Challis, continuing this corn- 



observation, one with telescope fixed and the other with parison, found that No. 49, a star of the 8th magnitude 



telescope moving. On July 30, the second day of the in the series of August 12, was wanting in the series of 



search, he observed by the second of these methods, and July 30. This was the planet, which had entered the 



on August 12, the fourth day of the search, he observed zone between July 30 and August 12. The former com- 



the same zone by the first method. Shortly afterwards parison had not been continued beyond No. 39 "probably 



he compared the observations of these days, in order to from the accidental circumstance that a line was there 



verify the adequacy of his course of procedure, and as far drawn in the memorandum-book in consequence of the 



as the comparison was carried, he found that the positions interruption of the observations by a cloud." 



