influence in the solar rays. 227 
Time of performing 
Extent of arc of vibra- 
Thermometer. 
40 vibrations. 
tion from zero at 
40th vibration. 
Observations previous 
r 63.0 
139.65 seconds. 
139.2 
1 5 0 00' 
13 OO 
to heating the com- 
j 
139-25 
13 OO 
pass-box. 
l 64.0 
>394 
13 OO 
1 
C/3 
zst time 
64.5 
I 4 I -3 
21 OO 
139.6 
12 45 
s . 
139-3 
12 30 
0 T 3 
CD 
QJ Cj 
pC a 
64.7 
1 39-5 
12 30 
2d time 
64.0 
141.6 
20 OO 
a § 
140.0 
15 OO 
cS _Q 
140.2 
P-t 
0 
0 
cl? 
63 -5 
140.0 
1 S 3 ° 
• H ^ 
cS x 
> 0 
3d time 
63*4 
141.4 
20 00 
rO 
O 
140.2 
*4 30 
.2 
! 39-6 
12 45 
O 
63.0 
139-7 
12 00 
These observations show clearly that an increased temper- 
ature on the compass-box tended to increase considerably the 
terminal arc, and that if the increased temperature, and con- 
sequent diminished intensity of the needle, had any tendency 
to diminish that arc, it was much more than counterbalanced 
by the effect produced on the compass-box. That such an 
effect should be produced on the brass is singular, and can, I 
think, only be accounted for on the supposition, that the 
capacity in brass for the developement of magnetism by 
induction is diminished by an increase of temperature, the 
vibrations of the needle being in all cases checked by the 
magnetism developed in the brass by the needle itself.* 
* Since making the foregoing observations I have found that a similar effect, 
arising, I conceive, from the same cause, is produced on a copper disc vibrating 
under the influence of a magnet : the number of vibrations required to reduce the 
