THE CENTENARY OF THE DISCOVERY OF URANUS. 
213 
of six satellites with, sidereal periods ranging from 5 d 21 h 25 m to 
107 d 16 h 39 ra , and his means of observation being much superior 
to those possessed by any of his contemporaries it was impossible 
to have corroborative testimony. 
The matter was thus allowed to rest until the middle of the 
present century, when Lassell, in the pure sky at Malta, en- 
deavoured to re-observe the satellites with a 2-foot reflector. 
This instrument was considered superior to Herschel’ s telescope ; 
and the atmosphere at this station being decidedly more suit- 
able for such delicate observations than in England, it was 
removed there for the express purpose of dealing successfully 
with objects of extreme difficulty. The results were very im- 
portant. Mr. Lassell became convinced that Uranus had only 
four satellites, and that if any others existed they remained to he 
discovered. Two of these were found to he identical with those 
seen by Herschel in 1787, and now called Titania and Oberon. 
The other two, Ariel and Umbriel, could not he identified with 
any of those alleged to have been previously detected by 
Herschel, so that the inference was that they were new bodies, 
and that the priority of discovery was due to Mr. Lassell ; 
whence it also followed that the older observations were 
erroneous, and that in fact Herschel had been entirely mis- 
taken with regard to the four satellites he believed he had 
detected subsequently to 1787. 
In November, 1873, a fine 26-inch object-glass, by Alvan 
Clark, was mounted at the TJ. S. Naval Observatory at Wash- 
