HERSCHEL. 217 



snn, from one to two liundred little i;)oints, remarkable by tbe briglituess 

 of their light ? Would it be possible for these little jjoiuts not to be 

 also distinguishable in the moon when it receives only the portion of 

 solar light which is refracted and colored by our atmosphere '? 



Hersehel 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 observation that if toward the 

 point of the horn there had been a deviation of only one second, occa- 

 sioned by the refraction of the solar light in the lunar atmosphere, it 

 would not have escaped him. 



He also made the planets the object of numerous researches. Mer- 

 cury was the one to which he gave least attention ; he found its disk 

 perfectly round on observing it during its projection — that is to say, in 

 astronomical language, during its transit over the sun, on the 9th of 

 November, 1802. He sought to determine the time of the rotation of 

 Venus as early as 1777. He published two memoirs relative to Mars, 

 the one in 1781, the other in 1781, and we owe to him the discovery of its 

 being flattened at the poles. After the discovery of the small planets, 

 Ceres, Pallas, Juno, and Vesta, by Piazzi, Olbers, and Harding, Her 

 schel applied himself to measuring their angular diameters. He concluded 

 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 criticised hj a historian of the 

 Eoyal Society of London, Dr. Thomson, who went so far as to suggest 

 that the learned astronomer •' had wished to deprive the first observers 

 of those bodies of all idea of rating themselves as high as himself in the 

 scale of astronomical discoverers." I should require nothing further 

 to annihilate such an imputation than to put it by the side of the fol- 

 lowing passage, extracted from a memoir by this celebrated astronomer, 

 published in the Philosophical Transactions for the year 1805 : "The 

 specific difference existing between planets and asteroids appears now, 

 by the addition of a third individual of the latter species, to be more 

 completely established, and that circumstance, in my opinion, has added 

 more to the ornament of our system than the discovery of a new planet 

 could have done." 



Although much has not resulted from Herschel's investigations in 

 regard to the physical constitution of Jupiter, astronomy is indebted to 

 him for several important results relative to the time of that planet's 

 rotation. He also made numerous observations on the distances and 

 comparative magnitude of its satellites. 



The compression of Saturn, the duration of its rotation, the physical 

 constitution of this planet and that of its ring, were, on the part of 

 Hersehel, the object of numerous researches ^vhich have much contributed 



