22 SEVENTH REPORT—1837. 
tion for 1830, p. 29. They gave the following results for the 
horizontal intensity at Christiania to unity in London: 
Needle IV Comparison in March . . 0°9124 
‘Comparison in May ... 0°9157 
VIII Comparison in March .. 0°9157 
‘Comparison in May... 0°9160 
33 
Mean... 09147 
We have seen that the observations in Paris and London 
gave |:0714 for the horizontal intensity at Paris, also to unity 
in London; consequently Christiania to Paris is as 09147 to 
10714, or as 0°8537 to 1. _In the spring of 1828 M. Hansteen 
observed the dip at Christiania 72° 16'2; at Paris at the same 
time, or about four months before August 1828, we may con- 
sider it to have been 67° 525. The total intensity at Christi- 
ania derived from this comparison is therefore 1:425, The 
result of a direct comparison between Paris and Christiania 
made by M. Hansteen in 1825 is 1°419. 
All the values of the intensity inserted in this memoir were 
originally observed in reference to one of these three stations, 
Paris, Christiania, or London, mediately or immediately, They 
have been united by means of the comparisons above noticed, 
viz., those of Paris and London, and of Paris and Christiania ; 
and they now form one connected series. 
Keilhau, 1827.—These observations were made in a voyage 
to Finmarken and Spitzbergen, in which M. Keilhau was fur- 
nished with an horizontal apparatus of M. Hansteen’s, and a 
5-inch dip circle and two needles made by Dollond. The 
observations were communicated to M. Hansteen, and the re- 
sults were published by him in the xivth vol. of the Annalen 
der Physik, from whence I have taken them. 
There may be remarked in these resuits greater differences 
of intensity between stations near to each other than are 
usually met with. From the geological character of the coun- 
tries, it is probable that a portion of these may be due to local 
circumstances; but it is also probable that a considerable por- 
tion of them may be attributed to the inadequacy of the dip- 
ping-needle with which M: Keilhau*was furnished, to give re- 
sults sufficiently exact for the computation of intensities, ina 
part of the globe where a small error in the dip will occasion 
a very considerable one in the deduced intensity. His two 
dipping-needles frequently gave results at the same station ~ 
differing from twenty to thirty minutes from each other. 
There are 20 stations determined by M. Keilhau in Norway, 
