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 Iris 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 



