147 



months, May, June, July, and August, a correction of +0'*8 in 

 compensation for annual variation, agreeably to an investigation con- 

 tained in the sequel. The Tables exhibit in every case the date, the 

 particular circle and needle employed, the azimuths in which the 

 observations were made, the name of the observer, the observed dip, 

 the reduction to a common epoch, the correction for annual variation, 

 and finally, the corrected result. 



The opportunity afforded at the Kew Observatory, of testing the 

 degree of accordance which may be expected in the results of different 

 instruments constructed on the plan which has been for several years 

 past approved and adopted at Kew, has thus been profited by, and the 

 conclusions appear such as to merit the consideration of those who 

 are desirous to possess reliable instruments. Several of the circles 

 are the property of foreign governments or of individuals, at whose 

 request they were provided subject to a verification at Kew. The 

 observations here recorded were for the most part made for the 

 purpose of such verifications, and were entered as they were made in 

 the books of the Kew Observatory, from which they are now taken. 

 No observation has been omitted. The circles were distinguished by 

 the numbers 20, 23, 27, 28, 30, 31, 33, 34, 35 and 36 ; and two 

 unnumbered, one known as the Kew Circle, the other an inclinometer 

 employed by Admiral Sir James Clark Ross in his recent magnetic 

 survey of a part of England. No. 20 was made for Professor Hansteen 

 of Christiania, and is now in his possession ; 23 is the circle used by 

 the late Mr. Welsh in his magnetic survey of Scotland ; 27 was 

 supplied to the Austrian frigate ' Novara ' for her voyage of circum- 

 navigation ; 28 was made for the Russian Government ; 30 was used 

 by myself in the recent magnetic survey of England, and has been 

 since supplied to the Observatory at the " Isle Jesus " near Montreal 

 in Canada; 31 was made for Padre Secchi of the Collegio Romano, 

 and is now at Rome ; 32 was made for the Rev. Alfred Weld of 

 Stonyhurst College, and is now in the Observatory of that College ; 

 34 was supplied to the Government of the United States of America, 

 and is now in the possession of Dr. Alexander Dallas Bache, Superin- 

 tendent of the Coast Survey ; Nos. 35 and 36 were made for the 

 Netherlands Government, one for Utrecht, and one for Java; the 

 "Kew Circle" was in regular use for the monthly determinations of 

 the Dip at Kew, from the commencement of those observations until 



