Biographical Memoir of Sir William' Herschel. &17 
In the year 1791, he measured with great accuracy the dimen- 
sions of the ring. He observed a variation in the light of the 
fifth satellite, and concluded that it moved round its axis in the 
same time that it revolved round the planet. He discovered,, 
in 1793, a quintuple belt, three of its component belts being 
dark, and two bright, and he soon afterwards determined the 
diurnal rotation of Saturn to be 10 h 16'. 
From the condition of the planetary bodies, Dr Herschel next 
proceeded to examine 44 The Nature and Construction of the Sun 
and the Fixed Stars f and he published the results of his obser- 
vations in the Philosophical Transactions for 1795. Consider- 
ing the surface of the sun as composed of luminous clouds float- 
ing in the solar atmosphere, and the dark nucleus of the spots 
as the opaque body of the sun seen through the openings in his 
atmosphere, Dr Herschel imagined that the functions of the 
great luminary, as the source of light and heat, may be per- 
formed by the agency of its external atmosphere alone, while 
the solid nucleus below, protected by clouds from the glowing 
element above, is possibly reserved and fitted for the reception 
of living beings. If this hypothesis be supported by no direct 
analogies, it may be attributed to the singular nature of the 
phenomenon it is formed to explain. It contains, at least, no- 
thing contrary to sound philosophy (which cannot be said of 
any of the wild speculations advanced on this subject by his 
predecessors) ; and the appearances of the solar disc are precisely 
such as ought to take place on the supposition of its truth. 
Such views serve to enlarge our conceptions of the Supreme 
Being, who, in every star that sparkles in the firmament, has 
dispensed the blessings of life and intelligence to various orders, 
of animated beings. 
In the year 1796, Dr Herschel communicated to the Royal 
Society his 64 Method of observing the Changes which happen to 
the Fixed Stars, with some Remarks on the Stability (f the 
Light of our Sun f to which he added 44 A Catalogue of Com- 
parative Brightness, for ascertaining the Permanency of the 
Lustre of Stars” This catalogue was followed in the same year 
by a Second Catalogue, along with remarks, tending to establish 
the rotatory motion of the stars on their axes ; in 1797 by a 
Third Catalogue of the same kind ; and in 1799 by a Fourth 
