862 
William Herschel.”' But the most considerable 
monument to Sir John Herschel’s love of science is 
the record of his four years’ labours for the advance- 
ment of Sidereal Astronomy at the Cape of Good 
Hope, where he applied his father’s methods of ob- 
Sir J. Her- servation to the southern hemisphere. His Results 
ae ob- of Astronomical Observations, which fill a large quarto 
gitke Caps volume, and which include “ the completion of a 
of Good Telescopic Survey of the visible Heavens, commenced 
Hope. in 1825,” form one of the most considerable and 
most interesting works of our time. The instruments 
employed were a 20-feet reflector, of 18} inches aper- 
ture, and a 7-feet achromatic, with 5 inches of aper- 
ture. With these the nebule and double stars of 
southern skies were examined and measured, and that 
wonderful “ Gauging of the Heavens” completed, of 
which I have spoken in the account of Sir William 
Herschel (201). There is an admirable chapter on 
the apparent magnitude of the stars, to which I shall 
refer presently, and one on Halley’s comet, besides 
other matters of interest. 
(295.) Since his return to England in 1838, Sir John 
His high fferschel has withdrawn from the labours of practi- 
character . 2 
amongst eal astronomy, but he continues to advance different 
his contem- branches of science, and to expound them by his able 
poraries. and lucid writings in a way which has made his au- 
thority equally respected by philosophers and by men 
of the world. The career of Sir John Herschel has 
been marked by an almost total absence of the ele- 
ment of ambition, so often a powerful excitement in 
MATHEMATICAL AND PHYSICAL SCIENCE. 
[Diss. VI. 
nected with the name of Sir John Herschel, from the 
ardour of his researches and the neatness of his 
methods. ‘To Savary of Paris is due the merit of 
ascertaining the form and position of the orbit of % 
Urse Majoris in 1827, which was followed by a 
more purely analytical method by M. Encke, and 
one chiefly graphical by Sir J. Herschel,? in which 
angles of position of the component stars are used 
nearly to the exclusion of the more doubtful measures 
of distance. On the whole, these investigations not 
only confirm Sir William Herschel’s anticipations, but 
render it highly probable that the relative orbits are 
really ellipses, and consequently that the law of force 
is that of the inverse square of the distance. The 
reader will find in Sir J. Herschel’s Cape Observa- 
tions a very curious discussion of the orbit of y Vir- 
ginis, a remarkable double star, whose interval was 
in 1788 five seconds and two-thirds, which diminished 
till 1836, when the two stars appeared united in one, 
as seen even in the best telescopes. This was the 
perihelion passage of these two suns, and the angle 
of position must then have varied (could it have 
been measured) at the rate of 70° per annum, or 1° 
in 5 days. 
certained periods of sidereal revolutions in years :— 
@ Herculis 36%-4; € Ursee Majoris 619-5; a Centauri 
77% ; p Ophiuchi 80 or 90%; ¢ Coronez Borealis 600 
or 700°. M. Midler, Admiral Smyth, and Mr Hind, 
have added much to our knowledge of this interest- 
ing subject. 
The following are some of the best as- « 
the pursuit of discovery. Had he sought notoriety 
and posthumous fame, he would have confined his 
efforts within a more circumscribed range. But his 
Brightness of Stars, and Variable Stars—Sir John (297.) 
Herschel has attempted by an elaborate system of?" ee 
inter-comparison to assign the'correct relative bright- of aaa 
versatile talents sought their appropriate exercise in 
all departments of exact science, and even (it is be- 
lieved) in pursuits widely distinct from these, in 
natural history, belles lettres, and the fine arts, In 
all this he no doubt considered simply the useful 
and pleasurable employment of his mental activi- 
ties. Truth seemed to him as desirable whether at- 
tained by the labours of others ‘or by his own; and 
in his numerous writings he has expounded these 
with a zest which a less generous ‘spirit might have 
reserved for his peculiar achievements. What he 
may have lost in future fame by this enlargement of 
his sympathies and interests, he has gained in the re- 
spect and good-will of all his contemporaries. Sir 
John Herschel recently filled the post of Master ‘of 
the Mint, to which, like his illustrious predecessor 
Newton, he devoted a considerable share of his time. 
His general eminence as a man of science has been 
acknowledged by his nomination in 1855 to the dis- 
tinguished honorary position of one of the eight fo- 
reign Associates of the French Academy of Sciences. 
(296.) Orbits of Double Stars—Though not absolutely 
= oe or- tho first ‘to apply calculation to the orbits of double 
paciid stars, this step in their theory may not unfitly be eon- 
stars. 
ness of the stars, and to give precision to the ordi- 
nary terminology of Magnitudes. His ‘ Method of 
Sequences” described in his Cape Observations, ap- 
pears to be one of the happiest specimens of generali- 
zation which experimental science affords. Whilst 
regretting the impossibility of here giving even the 
slightest sketch of it, I cannot but recommend it to 
the student of natural philosophy as a model of re- 
search. Having ascertained, in a way independent 
of every sort of hypothesis, the relative brightness 
of the stars upon the scale of Magnitudes usually 
adopted, but which is wholly arbitrary, Sir J. Her- 
schel proceeds, by properly photometric methods, to 
give a scientific precision to this notation; and he 
arrives at this singular and fortunate conclusion, that . 
by adding a small and constant correction to the re- 
ceived scale of Magnitudes, the numbers will repre- 
sent the distances of the respective stars from our 
system on the supposition of an intrinsic equality in 
the brightness of the stars themselves. 
This subject naturally includes that of Variable  (298.) 
Stars, which may be divided into those which under- Variable 
go periodic or irregular fluctuations, and the latter® 
class may embrace new stars, and stars which have 
2 Quarterly Review, vol. Ixxxv., p. 2. 
® Astronomical Society's Memoirs, vol. v. 
