(305.) 
Hender- 
son’s scien- 
tific pro- 
gress. 
Appointed 
to the Cape 
Observa- 
tory. 
(306.) 
The paral- 
lax of fixed 
stars, 
(307.) 
had been 
investi- 
gated by 
Pond and 
Brinkley. 
Notice of 
Brinkley, 
Bishop of 
Cloyne. 
864 
Majesty’s astronomer for Scotland, was born at 
Dundee, in Scotland, 28th December 1798. He died 
at Edinburgh 23d November 1844. His career was 
an instance of the conquest of disadvantages of many 
kinds by a patient, devoted, and conscientious spirit, 
and of the attainment of a station of great eminence 
in the world of science by singleness of purpose, and 
an ardent love of knowledge. 
He was fortunate in having Mr Duncan (now of 
St Andrews) as his instructor in mathematics at 
Dundee, and it was ‘* while employed as an attorney’s 
clerk in a provincial town that he laid the founda- 
tions of that extensive acquaintance with astronomy 
for which he was afterwards distinguished.” It was 
his good fortune to attract in Edinburgh the discern- 
ing notice of Sir James Gibson-Craig and his family; 
through whose influence, probably, he obtained pro- 
fessional employments of a kind which permitted 
him considerable leisure, and even gave him an op- 
portunity of forming scientific acquaintances in Lon- 
don. His early tastes were towards the practical cal- 
culations of astronomy, such as occultations and 
ephemerides; and from his merits alone he was 
commended and patronized by Dr Thomas Young. 
Had that great man lived, his promotion to a scienti- 
fic post would have probably been earlier. As it was, 
he obtained in 1831 an honourable, and, for him, 
lucrative appointment as astronomer at the Cape; at 
the sacrifice, however, of quitting his native country, 
In the thirteen months during which he held that 
situation, he performed an amount of first-rate work 
in practical astronomy which may bear a comparison 
with any similar effort. Charged with an instrument 
notoriously defective (Jones’s circle), he had to 
examine its errors and their compensations; and 
it is no small credit to him to say that with such 
an indifferent tool he carried off a prize which 
had been the aspiration of so many astronomers 
before him—the determination of the parallax of a 
fixed star. 
We must not go back to the history of this pro- 
blem previous to the nineteenth century, when alone 
instruments were so far perfected as to give results 
by which a parallax, or displacement by perspective 
of a star in consequence of the earth’s motion had a 
chance of being discovered, since it certainly does not 
amount to above a second or two, probably never 
attains even the former amount. 
The earlier part of this century witnessed a memor- 
able contest on this subject between Mr Pond, the 
Astronomer-Royal, and Dr Brinkley, afterwards Bi- 
shop of Cloyne; the former founded on observations 
MATHEMATICAL AND PHYSICAL SCIENCE. 
* [Diss. VI. 
at Greenwich, the latter at Dublin, both with instru- 
ments of great power, being meridian circles of the 
largest size. It is sufficient here to note that Dr 
Brinkley attributed to some of the brighter stars, 
such as @ Lyre, a parallax of 2":5 (which, how-: 
ever, he afterwards reduced to little more than 1”), 
whilst Mr Pond could arrive at no such result, There 
is no doubt that Mr Pond was correct. 
The first case of parallax which was determined with 
some certainty by the use of ordinary meridional in- 
struments was that of « Centauri, a bright star of the 
(308.) 
Henderson 
discovers 
that of a 
southern hemisphere, which was deduced by Hender- Centauri. 
son from his observations at the Cape long after they 
had been made, and what is perhaps still more satis- 
factory, made without reference to this particular 
question. The result, which gave to this star an 
annual parallax of 0-91 of a second, is believed to be 
correct, because it has been confirmed by Mr Maclear, 
Henderson’s successor at the Cape. It may, however, 
be not unreasonable to desire that the observations 
should be repeated in another locality, and with a 
different instrument; for it has not been unusual (as 
in the case of Brinkley) to obtain under the same _ 
circumstances perfectly consistent, yet erroneous, and 
therefore inexplicable results. 
The very considerable amount of parallax in this 
instance, corresponding to a large proper motion 
(3”°6), gives a strong independent probability that it 
is not materially erroneous ; and in this respect the 
most competent and impartial historians of science 
have given full credit to Mr Henderson for having, 
by superior skill in the use of his instruments, and 
the happy choice of an object, made a discovery which 
so many eminent observers had long sought for in 
vain. 
Subsequent to the date of Henderson’s observa- 
(309.) 
(310.) 
tions, but before their publication, Bessel (whose Bessel’s 
biography we have given in Section 3 of this chap- 
observa- 
tions on 61 
ter) determined the parallax of the star 61 Cygni, in cygni. 
a different way. It was a happy suggestion of Galileo, 
that if two stars be selected apparently near one 
another, but really disconnected, and having very un- 
equal magnitudes (therefore probably at very dif- 
ferent distances from our system),—and if the ap- 
parent angular distance between the two stars be 
measured from opposite parts of the earth’s orbit, 
it must sensibly vary by an obvious effect of per- 
spective. It was in pursuit of this happy idea 
that Sir W. Herschel discovered the fact that the 
connection of such pairs of stars is often real, not 
apparent—but it was Bessel who, guided in his 
choice of an object by the critical character of the 
1 John Brinkley, Bishop of Cloyne, was born in England, and educated at Cambridge, where he was senior wrangler in 1788. 
He acted for a short time as Maskelyne’s assistant at Greenwich, and was subsequently appointed Professor of Astronomy at 
Dublin, where he made many excellent observations, especially those on Nutation and Aberration. Brinkley ought to have 
been mentioned in Art. (30) of this Dissertation, as having contributed materially to the progress of the study of the Continental 
Mathematics iv the United Kingdom. 
