144 



Dr. T. E. Thorpe. 



The magnetic moment of the magnet before and after the survey 

 was as follows : — 



Mean. 



Kew, June 7, 1878.— I. 0-5592 

 II. 0-5592 

 Oct. 2, 1878. I. 0-5535 \ 

 II. 0-5534 J 



•5592 

 •5535 



The results of these observations compared with those of the Kew 

 unifilar made at about the same period are as follows : — 



Horizontal force. Diff. 



Kew Unifilar May 27, 1878. 3*8958 



Owens College Unifilar . Sept. 7, -„ r=3*9030 + 0*0074 



•1=3-9034 



Kew Unifilar . . . . Sept. 24, 1878. 3*8962 



Owens College Unifilar.. Oct. 2, „ r=3*9032 +0-0074 



l = 3-9041 



Combining these results with the respective values for the inclina- 

 tion obtained by the several instruments, we have the following in- 

 dependent determinations of the magnetic intensity, in absolute 

 measure, at Kew : — 



Horizontal. Vertical. Total. 

 Kew Instruments . . May, 1878. 3*896 9-516 10-283 



Owens College Instruments June „ 3*903 9*525 10'293 



Kew Instruments . .. Sept. „ 3*896 9-513 10-280 



Owens College Instruments Oct. „ 3*904 9*531 10*299 



Table IV shows the values in British units of the total force at 

 such of the above stations as are mentioned in Sir Edward Sabine's 

 " Contributions to Terrestrial Magnetism," ~No. XIII ("Philosophical 

 Transactions, 1872,") at the two epochs 1842*5 and 1878*7. 



Table IV. 



Pittsburg . . 

 New Haven 

 Chicago . . 

 Washington 



According to Mr. Schott, the horizontal force at Washington has 

 been steadily increasing since 1853*5. Prom observations made since 

 1842*5, he finds that the value of this element may be represented by 

 the formula 



X=4*270 + 0*00084 0-1855-0) +0*000248 (*-1855*0) 3 . 



1842-5. 



1878 -7. 



Dife. 



13*5 .. 



. 13*45 . . . 



. --05 



13-37 . . 



. 13-27 ... 



. --10 



13-78 . . 



. . 13-64 . . . 



. -14 



13-5 .. 



. . 13 25 . . . 



. -25 



