224 
Mr. Christie on magnetic 
Needle exposed 
to the sun; or 
being in shade. 
Thermometer. 
Time of performing 
40 vibrations. 
Extent of arc of vibra- 
tion from zero 
at 40th vibration. 
Times of commencing 
and of concluding 
the observations. 
- f 
72.5 
135.0 seconds. 
15 ° 
30 ' 
I l h 30 m 
•i ) 
75.0 
i 3 S-o 
14 
30 
1 
VD a 
75.0 
135 -° 
13 
3 ° 
l 
76.0 
! 34 - 8 
12 
00 
11 52 
Mean . 
74.6 
134-95 
13 
5 2 
. ( 
90.0 
135-3 
8 
00 
11 55 
§ < 
105.0 
1 3 5 *7 
9 
00 
w ) 
109.0 
136 2 
8 
30 
l 
1 12.0 
136.2 
8 
20 
12 12 
Mean . 
104.0 
I 35-85 
8 
27 
r 
87.0 
135-4 
1 2 
3° 
12 20 
84.0 
135-5 
14 
CO 
£ ) 
82.0 
135-3 
13 
00 
l 
81.0 
135-1 
12 
00 
12 40 
Mean . 
00 
04 
135 - 3 2 
12 
57 
Deducing the changes of intensity from the times of vibra- 
tion, the observations at 74 °.6 and 104° give .00045, and 
those at S3 0 . 5 and 104° give .00038 as the decrement in 
intensity corresponding to an increment in temperature of 
i°, one of the observations being in the shade, and the other 
in the sun in each case ; but from the observations at 74°.6 
and 83°.5, where both were made in the shade, we have 
.00061 : and again, from the observations at 90° and no°.5 
(the mean of 109° and 112 0 , the times of vibration at these 
temperatures being the same,) where both were made in the 
sun, we obtain .00064 as the decrement, the intensity at the 
lower temperature being in each case considered as 1. The 
small disagreement in the first two results may arise from 
errors in determining the temperature of the needle at the 
time of vibration, which, from the rapid changes that took 
