294 HERSCHEL. 
Royal Society of London, Dr. Thomson, who went so 
far as to suppose that the learned astronomer “had 
wished to deprive the first observers of those bodies, of 
all idea of rating themselves as high as him (Herschel) 
in the scale of astronomical discoverers.” I should re- 
quire nothing farther to annihilate such an imputation, 
than to put it by the side of the following passage, ex- 
tracted 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 com- 
pletely 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 hay- 
ing occupied himself with the physical constitution of 
Jupiter, astronomy is indebted to him for several im- 
portant results relative to the duration of that planet’s 
rotation. He also made numerous observations on the 
intensities and comparative magnitudes of its satellites. 
The compression of Saturn, the duration of its rota- 
tion, the physical constitution of this planet and that of 
its ring, were, on the part of Herschel, the object of nu- 
merous researches which have much contributed to the 
progress of planetary astronomy. But on this subject 
two important discoveries especially added new glory to 
the great astronomer. 
Of the five known satellites of Saturn at the close of 
the 17th century, Huygens had discovered the fourth ; 
Cassini the others. 
The subject seemed to be exhausted, when news from 
Slough showed what a mistake this was. 
