194 
LINES OF MAGNETIC DECLINATION IN THE ATLANTIC. 
The bearings were as follows : — 
N. 
S. 65° oo' W. 
s. 
S. 65 
oo' W. 
N.W. 
S.E. 
S. 63 
40 W. 
W. 
S. 67 00 W. 
E. 
S. 62 
00 W. 
s.w. 
S. 66 20 W. 
N.E. 
S. 62 
low. 
The correct magnetic bearing of the distant object from the ship (or that which 
would have been shown by the ship’s compass with her head on each of the points if 
there had been no local attraction) does not appear to have been observed ; we can 
obtain from the observations therefore only the differences of the bearings on the 
different points. From these we have the half difference of the bearings at east and 
west, 2° 30'=(nat. sine ’0436) =\/ at Moose Fort, where the (approximate) in- 
clination =8]°’00. Taking the value of the at Greenhithe in conformity 
with the observations there at ’025, and assuming that its variation should be as the 
tangent of the inclination, we should have -^^^^^^^^=’062 as its value at Moose 
Fort, if the change in the induced magnetism of the ship had kept pace with the 
change in the terrestrial dip. Here, as in other cases, the variation of 
was in arrear of the change of the inclination, since the observed value ’0436 corre- 
sponds to a dip of only 77° 13'. 
The whole amount of the deviation in the “ Prince Albert ” is, however, so extremely 
small in comparison with vessels of war (the extremes at the east and west points not 
exceeding at the Thames and 2 °^ at Hudson’s Bay), that we should obtain a 
sufficient approximation to the true variation of this term, whether we assumed it to 
vary with the change of dip, or uniformly with the lapse of time. I have taken the 
latter as the more convenient and ready mode ; increasing the coefficient from -}-'025 
on the 4th of June ’0002 per diem, to -l-’0436 on the 26th of August, and diminish- 
ing it at the same rate from the 9th of September, on which day the Prince Albert 
began to lower the dip on her homeward voyage, to the end of the month when she 
entered the British channel. 
Determinations in H.M.S. Rattlesnake in a passage from England to the Cape of Good 
Hope, in 1847, hy Captain Owen Stanley, R.N. 
The influence of the iron on the Rattlesnake’s standard compass was examined at 
Portsmouth, November 30, 1846, and again at Port Jackson in September 1847, 
circumstances having prevented a satisfactory repetition of the experiments during a 
short stay at the Cape of Good Hope. 
From the observations at Portsmouth in 1846, as subjoined, we obtain the values 
ofA=— 30'; D=-l-25', and E= -1-5'. 
