1878.] 



during Transit of Venus Expedition. 

 Table Y. 



5 



Station. 



m = magnetic 

 moment of 

 magnet. 



x= horizontal 

 force. 



y = vertical 

 force. 



z = total 

 force. 



Blackheath 



-45626 



3 -9107 



9 -5361 



10 -3068 





0-45595 



4 -3128 



6 -4039 



7-7208 



-45591 



4-3111 



6-4005 



7 -7170 





-45456 



4 -3056 



6-3930 



7 -7077 





-45406 



8 0354 



2-9425 



8 -5572 



„ Observatory. . . . 



-45456 



8 0849 



2 -8210 



8 -5629 





-45452 



8 -0841 



2 -8207 



8 -5621 





-45465 



8 -0869 



2 -8217 



8 -5650 





-45423 



7 -6289 



0-7304 



7 -6638 





0*45380 



7 '6216 



-7297 



7 -6565 



Port Said 



-45421 



6-4056 



5 -8762 



8 -6926 



Malta 





5 -6389 



7 "1175 



o -0805 





0-45390 



5 -4005 



7-5161 



9-2551 





0-45337 



5 -1451 



7 -9247 



9-4484 



Rome 



-45192 



4 -9144 



8 1435 



9 -5114 





0-45307 



4 -9269 



8 -1642 



9-5356 





0-45430 



4-7775 



8 3476 



9 -6181 





-45364 



4 -4755 



8-7566 



9 -8340 



The tables of Sir Edward Sabine (Phil. Trans., 1868) furnish very 

 few details from which to deduce the secular variation of the intensity 

 at the above stations. 



The total force at the Cape Observatory in 1845 was 7*58, and this 

 combined with 77152, the value for 1874, will give + 0-0047 as the 

 annual change. In the Cape Magnetic Observations, vol. i, we find 

 + 0*0066 as the corresponding value for 1848 u 



Taking the mean of the observations at Bombay in 1845 and 1847, 

 and also the mean for 1856 and 1867, we find 8*285 and 8*505 as the 

 values of the intensity for the epochs 1846 and 1861-5. Comparing 

 this last value with 8*5633 of 1875, gives a yearly change of 

 f- 0*0043, whilst the apparent change in 1854 was + 0*0142. Turning 

 now to the Colaba results from 1867 to 1873 we see that, for January 

 1st, 1871, the absolute value of the total force was 8*5391, with an 

 annual change of + 0*0064. This would make the magnetic intensity 

 8*5663 for April, 1875, which agrees well with the observed value. 

 The mean annual acceleration from 1861 to 1875 is considerably less 

 than the value deduced from the observations of the last few years. 



The intensity, 9*27, observed by Caligny at Malta in 1839, com- 

 bined with that of 1875, makes the annual variation — 0*0052. 



At Rome, 9*6575 in 1849 gives also an annual variation of — 0*0052 ; 

 but at Naples, 9'55 in 1845, makes the yearly change only — 0*0033. 



The Magnetic Decimation. 

 The observations, on which the determination of this element depend, 



