LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
37 
for deflector N, with those in the former table for the same deflector, and presu- 
ming that the values corresponding to the intermediate degrees change in a nearly 
uniform progression, we derive the following Table for the degrees of v' observed 
between the Cape and Kerguelen Island : — 
Values of w', deflector N, Terror; Cape of Good Hope 
to Kerguelen Island. 
O 
o S r - 
26 = -917 
33 = -873 
27 = -911 
34 = -866 
28 = -906 
35 = -859 
29 = *900 
36 = -852 
30 = -894 
37 = -845 
31 — -887 
38 = -837 
32 = -880 
39 = -828 
The Cape being the primary station, and its intensity = 0*715, we obtain the inten- 
sities at the other stations by the formula 
I' = *529 w' cosec v'. 
In the case of deflector S, the values of w' which result from the comparisons with 
the constant weights at the Cape and Kerguelen Island are so nearly the same (*733 
at the Cape, and *735 at Kerguelen Island), that we may take the arithmetical mean 
*/34 for all the intermediate stations without sensible inconvenience ; whence the for- 
mula for the calculation of the intensity becomes 
I' = *388 cosec v'. 
As we have only the comparisons with the constant weights at the Cape and Kergue- 
len Island from which to derive the values of w' for the Terror’s deflectors for all the 
intermediate degrees of v', we might be disposed to fear that the data were scarcely 
sufficient for that purpose ; but when we examine the intensities deduced from the 
observations with the two deflectors (both having been used at all the intermediate 
stations except one), we perceive that their accordance is in general remarkably good, 
which would scarcely be the case unless the elements of calculation were tolerably 
correct. So close an agreement in the partial observations, in a passage made in 
tempestuous weather, is certainly very creditable both to the instrument and to the 
observers. 
Those who interest themselves in examining the progress which magnetic maps of 
the portion of the globe occupied by sea are making towards accuracy, will compare 
the intensities between the Cape of Good Hope and Kerguelen Island, contained in 
the subjoined Tables, with the isodynamic lines drawn from Mr. Dunlop’s observa- 
tions in the first Number of these Contributions*. The prolongation of those lines 
into the more southerly latitudes traversed by the Erebus and Terror would suit ex- 
tremely well with the intensities which are here given. 
* Philosophical Transactions, 1840, Plate V. 
