18 
Mr. Christie on the effects oj tefnperature on 
Table of the Magnetic Intensities corresponding to different Tem- 
peratures of the Magnets. 
Mean Tempe- 
rature of tne 
Magnets. 
DifF. of Temp, 
in successive 
observations. 
Mean of the 
observed values 
of (p. 
Magnetic Inten- 
sity or value of 
F 
m’ 
DifF. of succes- 
sive values of 
F 
M ■ 
Variation of 
F 
for 1® Fah. 
M 
or A . , 
M 
o 
62.80 
61.08 
71.05 
65.95 
— 1.72 
+ 9-97 
—5.10 
0 t 
80 28 
81 14 
75 40 
77 44 
218.5687 
218.7269 
217.3014 
217. 9040 
4 0. 1582 
-f 1.4255 
-f 0.6026 
0.0920 
0. 1430 
0.1182 
There is only one, the first, of the values of A . which 
differs much from those already obtained, but the difference 
of the temperatures in the observations from which it is de- 
rived is so small, that any errors would be rendered very 
sensible ; and if the thermometers happened not to indicate 
the precise temperatures of the magnets at the times of ob- 
servation, it would be quite sufficient to account for this dis- 
crepancy. 
In his paper on the daily variation of the horizontal and 
dipping needles under a reduced directive power, Mr. Bar- 
low has described some anomalies which he observed between 
the daily changes in the direction of a needle when placed 
in the house and when in the open air, and also the steps 
which he took to discover their cause. He mentions, “ that 
in certain positions of the needle towards the east and west, 
the daily motion, although it proceeded with the same deter- 
minate uniformity in both cases, yet it took place in different 
directions ; passing in the one instance from the east, or west, 
towards the south, and in the other towards the north, at the 
