135 
Jam 29tli, Feb. 5th, Feb. 11th, March 16th, 
1867. 1867. 1867. 1867. 
C 1691-80 ...1690-04 ...1690-04 ...1690-04 
R 7-5 ... 7-5 ... 7-5 ... 10 
Rj 10 ... 10 ... 10 ... 12-5 
tan 6 -913087... *97852 ... *97520... -40610 
tan ... -379294... *40607 ... -40480... -20656 
t 2-8407 ... 2-7445 ... 2-7483 ... 2-7423 
L 2 -9679 ... 1-028 ... 1-0122 ... -9007 
r 185-976 ... 198*861 ... 198-303 ... 199*395 
T 3-6779 ... 3-6795 ... 3-6796 ... 3-6776 
The above determinations were obtained in a room in 
which there are several pieces of iron in fixed positions, and 
in the neighbourhood of which are some considerable masses 
of that metal. I have ascertained that these had an 
influence in increasing the intensity by about a fortieth. My 
current-meter, by which the horizontal intensity is immedi- 
ately deduced from a comparison of its weighings with the 
deflections of a tangent galvanometer included in the same 
circuit, shows a gradual increase of the intensity since last 
September, conformably with the results obtained in past 
years at Kew. 
“Note on the Tangent Galvanometer/’ by J. P. Joule, 
LL.D., F.R.S., &c., Y.P. 
It is well known that a current circulating round a 
magnetic needle produces a deflection of the latter, the 
tangent of which is approximately proportional to the 
strength of the current. Pouillet made the approximation 
much more close by using a broad strip of copper bent into 
a circle, instead of the usual coil, and thus obtained the 
instrument commonly known as the tangent galvanometer. 
The arrangement of Pouillet ensures a close approximation, 
it is true, but it does not, after all, exactly fulfil the law of 
