148 
MAJOR SABINE ON TERRESTRIAL MAGNETISM. 
F. 
Captain Frederick Beechey’s observations of the dip were made with a six-inch 
circle and needle by Robinson. 
Date. 
Poles. 
a. direct. 
/J reversed. 
Positions of the needle. 
Dip. 
Station. 
a . 
a'. 
a". 
a'”. 
1836. 
Feb. 20. 
Mar. 18. 
July 2. 
CL 
P 
a 
P 
CL 
P 
a 
0 
CL 
P 
— 13 28-2 
— 10 33-3 
— 23 42*7 
— 19 34*3 
— 23 38-5 
-19 51-6 
-38 27-7 
—36 06-2 
-38 45*4 
-36 10-1 
— 13 00*8 
-13 34-1 
-21 09-9 
-20 25*3 
-20 57*5 
— 21 11-2 
—37 55-6 
— 36 06-8 
-37 16-9 
-35 54-8 
— 13 27*5 
-13 18-6 
— 22 54-7 
-22 17-8 
-22 55-5 
—22 11-1 
-38 47*9 
— 35 56-1 
-38 20-9 
-36 17-4 
— 13 15*8 
— 12 37-1 
-22 06-2 
-21 06-5 
— 22 06-2 
-20 25-3 
-37 19-4 
-35 49 
— 38 02-2 
-36 06-9 
O / 
• -12 54 
• —21 40 
> -21 39 
- -37 03 
> -37 07 
i 
! 
Rio de Janeiro. 
>S'c. Catherine. 
^•Valparaiso. 
G. 
The observations of Captain Charles Drinkwater Bethune, R.N., were made 
with an instrument by Robinson of six inches diameter, furnished with two needles. 
The usual series of eight readings in different positions of the circle and needle were 
made, and the results are a mean of those given by the two needles. The readings 
in the different positions accorded well, as is usually the case in Robinson’s instru- 
ments. Captain Bethune’s report contains the details of the eight readings in each 
observation, but without specifying the positions to which they respectively belong. 
The results at the three stations employed in this paper are a part of an extensive 
series, chiefly in India and the Pacific Ocean, which will come under notice at a 
subsequent period, when observations now making in those quarters of the globe 
shall be completed ; the details of Captain Bethune’s observations at the three 
stations now employed will be more conveniently given at that time. 
H. 
The observations of Commander William Allen, R.N., were made with a circle of 
Jones with two needles, in both of which the readings, when the poles were changed, 
differed considerably. The results have been deduced by the known formula 
T tan M + tan M 7 
tan I = - — - — ^ ? 
wherein M is a mean of the readings in the usual four positions with the poles direct, 
and M' the same with the poles reversed. 
