TO THE OBSERVATORY SYNDICATE. liii 



that region. The second mode of observing required the aid of my two assistants, 

 Mr Morgan and Mr Breen, in reading off and recording the observations. 



I commenced observing July 29, employing on that day the first method, with 

 telescope fixed. The next day I observed according to the second method, with telescope 

 moving. On August 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 August 12, 

 the fourth day of observing, I went over the same zone, telescope fixed, as on July 30 

 with telescope moving. Soon after August 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 August 12, I felt convinced of the adequacy of the method of search I 

 had adopted. The observations were continued with diligence to September 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 approach of 

 daylight. On October 1, I heard that the planet was discovered by Dr Galle, at Berlin, 

 on September 23. I had then recorded 3150 positions of stars, and was making pre- 

 parations 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 August 12, I 

 found that No. 49, a star of the 8th magnitude in the series of August 12, was 

 wanting in the series of July 30. According to the principle of the search, this was the 

 planet. It had wandered into the zone in the interval between July 30 and August 12. 

 I had not continued the former comparison beyond No. 39, probably from the accidental 

 circumstance that a line was there drawn in the memorandum-book in consequence of 

 the interruption of the observations by a cloud. After ascertaining the place of the 

 planet on August 12, I readily inferred that it was also among the reference stars taken 

 on August 4. Thus, after four days of observing, two positions of the planet were obtained. 

 This is entirely to be attributed to my having, on those days, directed the telescope 

 towards the planet's theoretical place, according to instructions given in a paper Mr Adams 

 had the kindness to draw up for me. I would also beg to call attention to the fact that, 

 after August 12, the planet was discoverable by a closet-comparison of the observations, 

 a method of observing, depending on novel and ingenious mechanism, having been adopted 

 by which I could say of each star, to No. 48, " This is not a planet," and of No. 49, 

 " This is a planet." I lost the opportunity of announcing the discovery by deferring the 

 discussion of the observations, being much occupied with reductions of comet observations, 

 and little suspecting that the indications of theory were accurate enough to give a chance 

 of discovery in so short a time. On September 29, I saw, for the first time, the com- 

 munication presented by M. Le Verrier to the Paris Academy on August 31. I was 

 much struck with the manner in which the author limits the field of observation; and 

 with his recommending the endeavour to detect the planet by its disk. Mr Adams had 

 already told me that, according to his estimation, the planet would not be less bright 

 than a star of the ninth magnitude. On the same evening I swept a considerable breadth 

 in Declination, between the limits of Right Ascension marked out by M. Le Verrier, and 

 I paid particular attention to the physical appearance of the brighter stars. Out of 



