LABOURS RELATIVE TO THE SOLAR SYSTEM. 293 
illuminated, and opposite to the sun, from one to two 
hundred little points, remarkable by the brightness of 
their light ? Would it be possible for those little points 
not to be also distinguishable in the moon, when it re- 
ceives only the portion of solar light which is refracted 
and coloured by our atmosphere ? 
Herschel was more successful in his remarks on the 
absence of a lunar atmosphere. During the solar eclipse 
of the 5th September, 1793, the illustrious astronomer 
particularly directed his attention to the shape of the 
acute horn resulting from the intersection of the limbs of 
the moon and of the sun. He deduced from his observa- 
tion that if towards the point of the horn there had been 
a deviation of only one second, occasioned by the refrac- 
tion of the solar light in the lunar atmosphere, it would 
not have escaped him. 
Herschel made the planets the object of numerous 
researches. Mercury was the one with which he least 
occupied himself; he found its disk perfectly round on 
observing it during its projection, that is to say, in as- 
tronomical language, during its transit over the sun on 
the 9th of November, 1802. He sought to determine 
the time of the rotation of Venus since the year 1777. 
He published two memoirs relative to Mars, the one in 
1781, the other in 1784, and the discovery of its being 
flattened at the poles we owe to him. After the dis- 
covery of the small planets, Ceres, Pallas, Juno, and 
Vesta, by Piazzi, Olbers, and Harding, Herschel applied 
himself to measuring their angular diameter. He con- 
cluded from his researches that those four new bodies 
did not deserve the name of planets, and he proposed to 
call them asteroids. This epithet was subsequently 
adopted ; though bitterly criticized by a historian of the 
