144 Mr Christie on the Diurnal Variation 
Mean Temp, 
of the Mag- 
nets. 
Diff. of Temp, 
in successive 
observations. 
Magnetic In- 
tensity or Va- 
lue of 
M 
Variation of 
^forl°Fahr. 
M 
A F 
or A . — 
M 
49°30 
224.0981 
60.25 
4- 10.95 
222.8171 
0.1179 
68.25 
4- 8.00 
221.7046 
0.1391 
74.60 
+ 6.35 
220.7198 
0.1551 
61.75 
— 12.85 
222.3967 
0.1305 
73.80 
+ 12.05 
220.8778 
0.1260 
55.58 
222.6462 
66.00 
4- 10.42 
221.2655 
0.1315 
73.60 
+ 7-60 
220.1532 
0.1461 
56.90 
— 16.70 
222.5145 
0.1314 
A double series of observations on the diurnal changes in the 
positions of the points of equilibrium at which a magnetic needle 
was retained by the joint action of terrestrial magnetism and of 
two bar magnets, having their axes horizontal and in the mag- 
netic meridian, and their centres at the distance 21*21 inches 
from the centre of the needle, afford by correction and calcula- 
tion the following 
Tables of the Mean Terrestrial Magnetic Intensities at diffe- 
rent Hours during the Day. 
1. From observations made within doors. 
Time 
of 
Obser- 
vation. 
Mean of the Observations of 
May 22, 23, 24, 25, 26. 
Mean of the Observations of 
May 27, 28, 29, 30, 31. 
Mean of the 
two Sets. 
Azimuth of 
the points of 
Equilibrium. 
Terrestrial 
Magnetic 
Intensity. 
Azimuth of 
the points of 
Equilibrium. 
Terrestrial 
Magnetic 
Intensity. 
Terrestrial 
Magnetic 
Intensity. 
6 h 00 m 
7 30 
9 00 
10 30 
Noon. 
1 30 
3 00 
4 30 
6 00 
7 30 
9 30 
11 20 
81° 27.3' 
82 19.9 
83 13.9 
83 40.5 
82 22.8 
81 43.5 
81 29.1 
81 11.5 
81 17*7 
81 00.9 
80 52.6 
1.00175 
1.00100 
1.00031 
1.00000 
1.00096 
1.00151 
1.00173 
1.00199 
1.00190 
1.00216 
1.00229 
81° 56.9' 
82 27.4 
83 33.6 
84 16.2 
83 40.3 
82 39.5 
81 57.2 
82 10.8 
81 41.7 
81 20.5 
81 14.5 
81 19-7 
1.00170 
1.00128 
1.00046 
1.00000 
1.00038 
1.00112 
1.00170 
1.00151 
1.00192 
1.00224 
1.00233 
1.00225 
1.00173 
1.00114 
1.00039 
1.00000 
1.00067 
1.00132 
1.00172 
1.00175 
1.00191 
1.00220 
1.00231 
1.00225 
“ From the mean obtained here, it appears that the terrestrial 
magnetic intensity was the least between 10 and 11 o’clock in 
