Biographical Memoir of Sir William Herschel. 21 S 
was concerned. As the observations of double stars, however, 
presented great facilities for carrying on this inquiry, he devo- 
ted himself with much patience to the examination of this class 
of phenomena ; and, in the same year, he published, in the Phi- 
losophical Transactions , his “ Catalogue of Double , Triple , 
Quadruple , and Multiple Stars f a work which would have given 
immortality to an astronomer of any age. In order to measure 
the angular distance of two stars extremely near each other, he 
invented his Lamp Micrometer , which appeared in the Trans- 
actions of the same year. 
Dr Herschel’s attention was now directed to a subject of 
deep interest to astronomy. The celebrated Tobias Mayer was 
the first person who gave an explanation of the proper motion 
of the fixed stars, as first observed by Halley, and afterwards 
by Lemonnier and Cassini ; but the honour was reserved for 
Dr Herschel to point out the direction as well as the magnitude 
of their proper motion. By a comparison of the proper motion 
of the fixed stars, Dr Herschel discovered that the solar system 
is advancing to Hercules. He supposes that this motion is not 
rectilineal, but is performed round some distant centre, and 
though he has endeavoured to determine the velocity with which 
it moves, yet many ages must elapse before this inquiry can be 
crowned with complete success. The paper containing these in- 
vestigations, is published in the Transactions for 1783, and is 
entitled, “ On the Proper motion of the Sun and Solar System , 
with an account of several changes that have happened among 
the Fixed Stars since the time of Mr Flamstead^ 
Between the years 1777 and 1783, Dr Herschel made some 
interesting discoveries respecting the planet Mars. The lumi- 
nous zone which had often been observed at the southern pole 
of the planet, he found to arise from the reflection of the sun’s 
light, from its frozen regions. In 1781, when its polar zone had 
not experienced the influence of the sun for twelve months, the 
south polar spot was of great magnitude, and in 1783 it had 
suffered a very great diminution from an exposure of eight 
months to the solar rays. Our author likewise determined, that 
the equatorial was to the polar diameter of the planet as 16 to 
15 nearly, and that the period of his daily revolution was about 
24< h 39'. These curious results were communicated to the Royal 
