316 ADDRESS ON PRESENTING THE GOLD MEDAL OF THE [42 



than has been generally entertained. Bradley himself remarked, that Flam- 

 steed's observations of the pole-star agreed with his theory of aberration. 



The celebrated controversy between Brinkley and Pond is discussed at 

 considerable length, and the labours of the latter astronomer are criticised 

 with great severity. M. Peters considers that Brinkley was far superior 

 to his opponent in his knowledge of the theory of his instruments, and 

 in the use of precautions to avoid error, though it is certain that Pond 

 was the more correct in his conclusions respecting parallax. 



The parallaxes determined by M. Struve at Dorpat, from 1818 to 1821, 

 by means of observed differences of right ascension of circumpolar stars 

 having nearly opposite right ascension, deservedly occupy a good deal of 

 attention. The parallaxes thus found, though small, were almost all positive, 

 and M. Peters confirms their reality by the following ingenious consideration. 

 He shews that any diurnal variation of the instrument due to temperature 

 will affect the coefficients of aberration and parallax in the same direction, 

 and the former probably more than the latter. Now, the coefficient of 

 aberration found from these observations is about 0"'08 less than the 

 definitive value given by the Pulkowa observations, and it is therefore 

 probable that M. Struve's parallaxes should be increased by a few hundredths 

 of a second. 



It is unnecessary for me to follow M. Peters in his account of Struve's 

 micrometrical measurements of the parallax of a Lyra, of Bessel's well- 

 known observations of 61 Cygni with the heliometer, and of the parallaxes 

 of a Centauri and Sirius, as determined by MM. Henderson and Maclear 

 at the Cape, as these have been fully discussed by Mr Main in an able 

 paper in the twelfth volume of our Memoirs. The Council is also indebted 

 to Mr Main for a careful report on M. Peters' paper, from which I have 

 derived considerable assistance in drawing up my account of it. 



The second and most important part of M. Peters' paper consists of 

 an investigation of the parallaxes of eight stars, by means of observations 

 of zenith distance made by M. Peters at Pulkowa, in 1842 and 1843, with 

 Ertel's great vertical circle. The stars selected are Polaris, Capella, i Ursa 

 Majoris, Groombridge 1830, Arcturus, a. Lyrce, a. Cygni, and 61 Cygni. 



The utmost care is taken in the instrumental adjustments, in the 

 equalisation of the interior and exterior temperatures, and in eliminating 

 every imaginable source of error. 



