Prof. Challis's Observations relative to the Neiv Planet. 39 



the first method, with telescope fixed. The next day I ob- 

 served according to the second nietliod, with telescope moving. 

 On Aug. 4, the telescope was fixed as to right ascension, but 

 was moved in declination in a zone of about 70' breadth, the 

 intention of the observations of that day being to record points 

 of reference for the zones of 9' breadth. On Aug. 12, the 

 fourth day of observing, I went over the same zone, telescope 

 fixed, as on July 30 with telescope moving. Soon after, 

 Aug. 12, I compared to a certain extent, the observations of 

 that day with the observations of July 30, taken with telescope 

 moving ; and finding, as far as I carried the comparison, that 

 the positions of July 30 included all those of Aug. 12, I felt 

 convinced of the adequacy of the method of search I had 

 adopted. The observations were continued with diligence to 

 Sept. 29, chiefly with telescope fixed, and were made early in 

 right ascension for the purpose of exploring as large a space 

 as possible before I should be compelled to desist by the ap- 

 proach of daylight. On Oct. 1, 1 heard that the planet was 

 discovered by Dr. Galle at JBerlin, on Sept. 23. 1 had then 

 recorded 3150 positions of stars, and was making preparations 

 for mapping them. The following results were obtained by 

 a discussion of the observations after the announcement of the 

 discovery. 



On continuing the comparison of the observations of July 

 30 and Aug. 12, I found that No. 49, a star of the 8th mag- 

 nitude in the series of Aug. 12, was voanting in the series of 

 July 30. According to the principle of the search, this v/as 

 the planet. It had wandered into the zone in the interval 

 between July 30 and Aug. 12. I had not continued the for- 

 mer comparison beyond No. 39, probably from the accidental 

 circumstance that a line was there drawn in the memorandum 

 book in consecjuence of the interruption of the observations 

 by a cloud. After ascertaining the place of the planet on 

 Aug. 12, I readily inferred that it was also among the refer- 

 ence stars taken on Aug. 4. Thus, after four days of obser- 

 ving two positions of the planet were obtained. This is en- 

 tirely to be attributed to my having on those days directed 

 the telescope towartis the planet's theoretical place, according 

 to instructions given in a })aper Mr. Adams had the kindness 

 to draw up lor me. I would also beg to call attention to the 

 fact, that, after Aug. 12, the planet was discoverable by a closet- 

 comparison of the observations; a method of observing, de- 

 pending on novel and ingenious mechanism, having been 

 adopted, by which I could say of each star, to No. 48, ' This 

 is not a plancl,' and of No. 49, ' This is a planet.' I lost the 

 oppoitunily of announcing the discovery by deferring the dis- 



