Royal Society. 71 



but his misquotations and errors are numerous, so that as a work 

 of reference it is valueless. The Astronomer Royal's discovery of 

 the inequality of the motions of the Earth and Venus, the period 

 of which is 240 years, is ascribed to Le Verrier, with not one word of 

 the laborious work of the Astronomer Royal. The work concludes 

 with the announcement that it is demonstrable that the area of the 

 circle is equal to three fourths of the square of its diameter. 



IX. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from vol. xli. p. 546.] 



March 9, 1871.— General Sir Edward Sabine, K.C.B., President, 

 in the Chair. 

 fpHE following communication was read : — 



-*- " Results of Seven Years' Observations of the Dip and Hori- 

 zontal Force at Stonyhurst College Observatory, from April 1863 to 

 March 1870." By the Rev. S. J. Perry. 



The object of the present paper is to bring further evidence to 

 bear upon an important question of terrestrial magnetism. 



The existence of a sensible semiannual inequality in the earth's 

 magnetic elements, dependent on the position of the sun in the 

 ecliptic, was deduced by General Sir Edward Sabine from a dis- 

 cussion in 1863 of a continuous series of the monthly magnetic ob- 

 servations taken at Kew. A previous reduction of observations made 

 at Hobarton and at Toronto had first suggested the idea, and a new 

 confirmation of the results has lately been obtained by Dr. Balfour 

 Stewart from subjecting a second series of Kew observations to the 

 same tests as before. The observations, which form the basis of 

 the present discussion, extend over the period from March 1863 to 

 February 1870, during which time the same instruments have been 

 in constant use. These are a Jones unifilar and a dip-circle by Bar- 

 row, both tested at Kew, and a Frodsham chronometer. Sir Edward 

 Sabine, who made the Stonyhurst Observatory one of his magnetic 

 stations in the English survey in 1858, greatly encouraged the 

 undertaking of monthly magnetic observations, and the Rev. A. Weld 

 procured in consequence the instruments still in use. Only occa- 

 sional observations were made with these instruments for some years, 

 and it was only in 1863 that a continuous series of monthly deter- 

 minations of the magnetic elements was started by the Rev. W. 

 Sidgreaves. He observed regularly until September 1868, when I 

 returned to my former post at the Observatory, and I have continued 

 the same work ever since. 



A stone pillar was at first erected for the magnetic instruments 

 in the open garden, and this remained in use from 1858 until the 

 beginning of 1868, when a most convenient hut of glass and wood 

 was built for the instruments in a retired corner of the College garden. 

 This alteration was rendered necessary from the placing of iron rails 

 in the vicinity of the old pillar ; and although it introduces into the 



