LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
25 
Table I. (Continued.) 
Position. 
Deflection 
g 
Ship’s head. 
Intensity. 
1840. 
Time of day. 
Method employed. 
observed. 
S3 v 
Lat. 
Long. E. 
H ^ 
London = 
= 1-000. 
= 1-372. 
s. 
35 09-1 
O 
79 
s. 
*729 
MarchSO. 
Moored 
in Si- 
s. 
35 16-2 
76 
s.w. 
•726 
mon’s 
Bay. 
s. 
35 39-1 
w. 
•713 
34 11 
18 26 
s. 
35 50-7 
N.W. 
•710 
s. 
35 45-6 
N. 
•712 
s. 
35 48-9 
N.E. 
•711 
s. 
35 38-6 
E. 
•715 
Block House 
s. 
35 39-3 
80-5 
f -7i5 q 
Simon’s Bay. 
S. and N. 
51 06-4 
80*5 
•716 
Noon. 
N. 
29 54-2 
80-5 
•714 
weight 1 grain. 
14 48-9 
87-5 
•719 
25. 
8 A.M. 
weight 1| grain. 
S. 
22 57-8 
35 40-8 
87-5 
80-5 
, Observed 
on shore. 
< 
•709 
•715 
>•715 
•981 
S. and N. 
51 13*5 
80-5 
•714 
N. 
29 51-5 
80-5 
•716 
weight 1 grain. 
15 20-6 
92 
•695* 
weight 1| grain. 
22 42-4 
91 
L -715 J 
Observations in the Terror . — The observations in the Terror were made with a 
Fox’s needle of four inches diameter ; one of equal size with that in the Erebus, 
which was not ready when the Expedition sailed, having been sent out subsequently, 
and received by Captain Crozier, at Van Diemen Island, in August 1840. An in- 
strument of only two inches radius, for the purpose of determining both the dip and 
intensity at sea, might previously have been regarded by many persons as scarcely 
more than a philosophical toy ; and as little likely to yield results having the preci- 
sion which is now required in such determinations. It has, however, in Captain 
Crozier’s hands, fully justified the expectations which Mr. Fox, from his own expe- 
riments with it, had ventured to entertain. On land, the instruments of the Erebus 
and Terror are, for the most part, as far as they have yet reached us, nearly identical 
in their results. Confining our attention to the intensity as the subject immediately 
before us, the intensities at James Town in St. Helena, and at Longwood in the same 
island, measured by the instruments of the two ships, the days and spots of observa- 
tion being the same, are by the Erebus in the proportion of *586 at Longwood to 
•611 at James Town, and by the Terror as *587 to *611. The agreement is in this 
case the more valuable, because we are justified by it in ascribing the difference thus 
found between places so geographically near to each other, to a really existing differ- 
ence (viz. to station error), rather than to accident or to observation error, as might 
have been done, had only a single instrument been used. A similar accord in the de- 
terminations of the two instruments is shown by the results at the Cape of Good Hope 
and Kerguelen Island, which, though more properly belonging to the next section, 
may be instanced here in evidence of the confirmation which the two instruments 
MDCCCXLII. 
* Omitted in the mean. 
E 
