influence in the solar rays. 
229 
1 
Thermometer. 
Time of performing 
30 vibrations. 
Extent of arc of vibra- 
tion from zero at 
30th vibration. 
The needle having been 
63° 
99.9 seconds. 
5 0 1 5' 
re-magnetised previ- 
99.8 
5 3° 
ous to immersion in 
99-7 
5 3° 
boiling water. 
99-7 
5 3° 
Mean 
99-775 
5 26 
63 
104.2 
6 00 
The needle having been 
104.15 
6 15 
immersed in boiling 
104.25 
6 15 
water. 
104.4 
6 15 
Mean 
104.25 
6 1 1 
The needle having been 
63 
100.2 
6 15 
re-magnetised after 
100.4 
6 30 
immersion in boiling 
100.3 
6 30 
water. 
100.4 
6 45 
Mean 
100.325 
ON 
cw 
0 
The increase here in the terminal arcs being gradual, and 
taking place under opposite circumstances, appears to have 
arisen from the friction on the pivot being gradually dimi- 
nished. Taking a mean of the arcs before immersion and 
after it, when the needle had been re-magnetised, it is rather 
less than the mean arc when the intensity of the needle was 
reduced by an increased temperature arising from the immer- 
sion ; so that an increase of temperature which diminished 
the intensity of the needle from 1 to 0.92, produced no sen- 
sible effect on the terminal arc. The decrease of intensity is 
here much greater than any that could arise from an increase 
of temperature derived from the direct rays of the sun ; it is 
therefore manifest from these last experim ents, independent 
of any thing which I have before stated, that the heat of the 
sun, by diminishing the intensity, could not be the cause of 
MDCCCXXVI. H h 
