192 History of the Discovery of the Planet Neptune. 
rier was proceeding with his computations, and on the 31st of 
August, he announced to the Academy the elements he had ob- 
tained for the supposed planet. He assigned its exact place in 
the heavens, and estimated that it should appear as a star of the 
eighth magnitude, with an apparent diameter of about three se- 
conds; and consequently that the planet ought to be visible in 
good telescopes, and with a perceptible disc. 
Soon after this communication was made to the Academy, Le 
Verrier wrote to Dr. Galle of the Berlin Observatory, (where is 
found one of the largest telescopes of Europe,) requesting him to 
undertake a search for his computed planet, and assigning its sup- 
posed place in the heavens. The Berlin Academy had. just pub- 
lished a chart of this part of the heavens, showing the exact place 
of every star down to the tenth magnitude. On the evening of 
the very day upon which this letter was received, (September 23, ) 
Galle found near the place computed by Le Verrier, a star of the 
eighth magnitude not contained on the Berlin charts. Its place 
was carefully measured ; and the observations being repeated on 
the succeeding evening, showed a motion of more than a minute 
of space. The new star was found in longitude 325° 52’; the 
place of the planet computed by Le Verrier was 324° 58’: so 
that this body was within one degree of the computed point. Its 
diameter measured nearly three seconds. A coincidence so exact 
left no doubt that this was really the body whose effects had been 
detected in the motions of Uranus. The news of the discovery 
spread rapidly over Europe. The planet was observed at Gottin- 
gen on the 27th of September, at Altona and Hamburgh on the 
28th; and at London on the 30th. 
We must now return to Professor Challis, whom we left explo- 
ing a large zone of the heavens, and recording the exact position 
of every star down to the eleventh magnitude. These observa- 
tions were continued from the 29th of July to the 29th of Sep- 
tember, during which time he had made more than three thou- 
sand observations of stars. On the 29th of September, Professor 
Challis saw for the first time, Le Verrier’s memoir communica 
to the Academy, August 31st. Struck with the confidence which 
Le Verrier manifested in his own conclusions, Professor Challis | 
immediately changed his mode of observation, and endeavored. 
to distinguish the planet from the fixed stars by means of its disc. 
n the same evening he swept over the zone marked out by Le © 
Verrier, paying particular attention to the physical appearance of 
the brighter stars. Out of three hundred stars whose positions 
were recorded that night, he selected one which appeared to have 
a disc, and which proved to be the planet. On the first of Octo- 
ber he heard of the discovery at Berlin; and now on comparing 
his numerous observations, he finds that he had ¢wice observed 
the planet before, viz., on August fourth and twelfth; but he lost 
