66 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



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. 



(305.) He was fortunate in having Mr Duncan (now of 

 Hender- g^ Andrews) as his instructor in mathematics at 

 tific pro- Dundee, and it was " while employed as an attorney's 

 gress. 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- 

 Appointed fi c 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. 

 (306.) We must not go back to the history of this pro- 



The paral- |j] em previous to the nineteenth century, when alone 

 lax of fixed . , , . Ji . ,. 



stars, instruments were so tar 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. 



(307.) The earlier part of this century witnessed a memor- 

 had been a k] e con test on this subject between Mr Pond, the 

 gated by Astronomer-Royal, and Dr Brinkley, afterwards Bi- 

 Fond and shop of Cloyne ; the former founded on observations 

 Brinkley. 



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 a Lyrse, 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. 1 



The first case of parallax which was determined with (308.) 

 some certainty by the use of ordinary meridional in- Henderso: 

 struments was that of a Centauri, a bright star of the 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 (309.) 

 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- (310.) 

 tions, but before their publication, Bessel (whose Vessel's 

 biography we have given in Section 3 of this chap- tj^on'g 

 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 reaZ, not 

 apparent but it was Bessel who, guided in his 

 choice of an object by the critical character of the 



Notice of 

 Brinkley, 

 Bishop of 

 Cloyne. 



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 in the United Kingdom. 



