LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
Ill 
to bring them into strict relation with 1*82, taken as the value of the force at Hobarton. 
This correction being applied, all the intensities observed throughout the voyage by 
the two ships are in accordance (subject only to errors of observation), forming a 
consistent series of relative determinations, resting on T82 and T336, assumed 
provisionally as the values of the intensity at Hobarton and Port Louis, the com- 
mencing and concluding stations of the series. The correction is made in the Table 
which exhibits the intensities observed on board the two ships, and the geographical 
positions to which they belong ; it is also made in the results inserted in the Map. 
The correctness of the values assumed at the base stations, 1*82 at Hobarton and 
1*336 at Port Louis, remains to be proved by absolute determinations which have yet 
to be made at those two stations. The absolute intensities observed by the Expedi- 
tion itself, with the instruments and according to the method prescribed in the 
instructions of the Royal Society, certainly have not the necessary precision. In the 
preceding Number of these Contributions are stated the results of five determinations 
which were obtained by Captain Ross at Hobarton in 1840 and 1841, with the 15-inch 
magnets of his observatory magnetometers; and of twenty- two determinations obtained 
bv Lieut. Kay at the magnetic observatory at that station, with similar instruments, 
in 1841 and 1842. Captain Ross’s mean result was 4*573, the partial results 
varying from 4*491 to 4’626. Lieut. Kay’s mean result in 1841 was 4*553, the partial 
results (ten in number) varying from 4*509 to 4*601 ; and in 1842 4*513, the partial 
results (twelve in number) varying from 4*443 to 4*568. In 1843 Lieut. Kay received 
the auxiliary apparatus supplied in compliance with the revised instructions of the 
Royal Society, published in 1842. The magnets of this apparatus were 12 inches in 
length. The following Table exhibits the results obtained with this instrument in 
thirteen determinations made with it, between June 23rd and July 1st, 1843. Each 
determination is deduced from two series of observations of deflection ; in the first 
six instances the distances were 4*505 and 6*005 feet ; in the remainder, 4*0 and 5*3 
feet. The moment of inertia of the deflecting magnet was computed from the length, 
breadth and mass of the bar. 
June 23. 
4*509 
June 2 7. 
4*557 
24. 
4*515 
28. 
4*505 
24. 
4*528 
28. 
4*504 
26. 
4*510 
29. 
4*549 
26. 
4*523 
29. 
4*527 
27 * 
4*583 
30. 
4*466 
July 1. 
4*479 
Mean of the 13 determinations 4*520 
Here also it is obvious, from the discrepancy of the partial results, that the angles 
of deflection afforded by these magnets at the prescribed distances, viz. the least 
distance being not less than four times the length of the bar, were still too small; and 
that before any final conclusion be arrived at, it is desirable that we should await the 
MDCCCXLIV. Q 
