OBSERVATIONS ON THE MAGNETIC FORCE. 
CXXX111 
1820, December. In the Regent’s Park, London, Latitude 51° 31' N., Longitude 
0° 08' W. Dip 70° 33'. 3 N. 
IN THE MAGNETIC 
MERIDIAN. 
No. of 
Vibrations 
Interval 
> 
o 
p-i 
o 
o 
CO 
CO 
CD 
CD CD 
CO | 
M S 
a 
vf 
100 
S 02 
100 
100 
7 58 
S 00 
Arcs 
o 
70 
46 
36 
CO 
pH 
CD 
pH 
<N 
i-H 
9 
7 
5 
CO 
o 
o 
o 
O 
o 
o 
O 
o o 
o 
100 
8 00 
Mean 
£ 2 
£-2 
> 
pH 
pH 
pH 
I-H 
r-H 
rH 
pH pH 
pH 
WITH NEEDLES SUSPENDED HORIZONTALLY. 
The Needles used in these Experiments were bars of Steel of seven inches 
in length, 0.25 in breadth, and 0.15 in thickness, magnetized to saturation 
previous to the voyage, and their magnetism not interfered with subsequently. 
Three such bars had been provided, numbered from 1 to 3, whereof 
Nos. 2 and 3 were kept together when not in use, with their opposite poles 
connected; No. 1 was kept by itself. 
Each of the Needles successively was placed for use in an instrument 
made for the occasion ; consisting of a circular plate of ten inches diameter, 
centred as usual, and adjusted horizontally by foot screws, as shewn by 
spirit levels fixed at right angles to each other ; a graduated ring, eight 
inches in diameter, was attached to the plate, and rose half an inch above it ; 
on the outside of the ring were three pillars nine inches in height, bearing a 
tripod, from the centre of which, a stirrup was suspended by a silk line. 
The needle being slid into the stirrup until it balanced horizontally, and 
being left to itself, and the instrument protected from the air by a bell-glass, 
it indicated, on settling, the Magnetic Meridian. The brass plate was then 
