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HISTORY OF PHYSICAL ASTRONOMY.
and published. The Berlin astronomers received Le Vender's letter onthe 23rd September. On the same evening Dr. Galle compared theappearance of the heavens with the map, and found that the latter did notcontain a star of the eighth magnitude which was situate very near the placeindicated by Le Verrier as the locus of the disturbing body. The observa-tions of the following evening decided that this was the Trans-Uranianplanet. It was then retrograding with a daily motion in right ascensionamounting to 62". The following is a comparison of the results of obser-vation and theory.
Observed Right Ascension 23rd September, I2 h 0 m 15 s
M. T. Berlin. 328° 19'16"
Observed Declination South.13" 24' 8"’2
Whence—
Geocentric Longitude ...... 325° 53'
True Heliocentric Longitude ..... 326° 57'
Longitude for the same instant, assigned by Le Ver-
rier’s theory ....... 326° O'
Difference between Observation and Theory . . 57'
Thus it appears that the place assigned by Le Verrier to the disturbingbody did not differ by so much as one degree from its actual place as in-dicated by observation. Nor was the agreement less striking with respectto the apparent diameter of the planet. Le Verrier had predicted that itwould be equal to 3".3 ; the micrometrical observations of the Berlinastronomers gave 3" as the real value.
The accounts of the discovery of the Trans-Uranian planet were re-ceived with admiration and delight by all who felt any interest in thecause of science, and the name of Le Verrier was henceforth associatedwith those illustrious philosophers who have stamped the age in whichthey lived with the impress of their genius. We shall now give a briefaccount of the labours of Professor Challis, who had undertaken a verylaborious examination of the heavens in search of the planet. We havementioned that he commenced his observations on the 29tli July. His planwas to divide the region to be explored into zones of 9'in declination, thisbeing the breadth of the field of view of the telescope when a magnifyingpower of 166 was employed, and to note the positions of all the stars iiieach zone down to the eleventh magnitude. On the 4th August his obser-vations were made wholly in declination, for the purpose of obtaining anumber of stars as reference points. On the 12th of the same month henoted the positions of all the stars in a zone which he had already ex-amined on the 30th July. He compared to a certain extent the observa-tions of the two evenings, and, having discovered their complete accord-ance, he felt assured that his method of search might be relied upon. Hecontinued his observations throughout the months of August and September.On the 1 st October he was made acquainted with the discovery of the planetby Galle. He had then recorded the positions of 3150 stars, and was makingpreparations to map them. The necessity for this operation having ceased,he proceeded to discuss the observations, with the view of ascertaining