368 



Rev. S. J. Perry on Magnetic 



[Mar. 9, 



of Vibration," by which I made all my observations on the submarine boat 

 and on armour-plated ships. In this instrument the needle is 3*2 inches 

 long and 0*17 inch in breadth. 



The magnet is suspended on a silk thread and vibrates in a wooden box, 

 on the side of which there are the divisions in degrees to mark the angles 

 formed by the turning-needle ; for each observation I counted 700 vibra- 

 tions. I found that for such a voyage this instrument answers the purpose. 



The exact drawing of this instrument you will find in my book on the 

 " Submarine Boat/' 1867, Plate VI. Drawings 6 and 8 give half the size 

 of the instrument, and drawing 7 the full size of the needle. 



I know that General Sabine and the Royal Society are much interested 

 now in the Northern Magnetic Observations, so I hastened to send the 

 results to you, as I know that they cannot he printed soon in Russian. 



I remain, your attached friend, 



John Belavenetz. 



4 



Oonstadt, ^ November, 1870. 



March 9, 1871. 



General Sir EDWARD SABINE, K.C.B., President, in the Chair. 

 The following communications were read : — 



I. "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. Communi- 

 cated by the President. Received January 23, 1871. 



(Abstract.) 



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 mag- 

 netic elements, dependent on the position of the sun in the ecliptic, was 

 deduced by General Sir Edward Sabine from a discussion in 1863 of a 

 continuous series of the monthly magnetic observations 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 

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

 Sabine, who made the Stonyhurst Observatory one of his magnetic stations 



