65 
of the Radiation of Heat in the Atmosphere. 
can enter into comparison with Mr Daniell's. A mercurial ther- 
mometer, having its bulb blackened, and covered with black 
wool, w r as fully exposed to the sun, on grass. The following 
are the results obtained at Bahia : 
July 24. 
114° 
July 28. 
95' 
25. 
123 
29. 
115 
26. 
124 
30. 
12T 
27. 
123 
These results were obtained during a southerly wind, with 
frequent rain, surely not the most favourable weather for such 
experiments. At Jamaica, with the same thermometer, the 
highest temperature observed was 123° ; but no remarks are 
given on the state of the weather. M. Gay Lussac objected 
to these experiments, as having been influenced by the vegeta- 
tion on which the instruments reposed. As Mr Daniell rests 
the truth of his opinion chiefly on these experiments, we made a 
few trials, to ascertain the probable amount of such effects upon 
the results. On the 7th of July last, temp, of the air 59°, with 
brisk wind, we exposed a large thermometer, having its ball co- 
vered with black wool, to the direct rays of the sun, but not 
sheltered from the wind. In 10' it rose to 95°. It was then laid 
flat on short grass, when it fell to 60° ; and on replacing it in its 
former position, in 4' it again rose to 94°. On the 29th of the 
same month, at 10' before 3 p. m., the same thermometer which 
had been exposed all day in a sheltered corner, rose to 150°. 
At the same instant another instrument, similarly prepared, and 
resting in contact with the herbage, indicated only 119°. Again, 
on the 29th, at 2 p. m., the first thermometer as before, was at 
140°, #nd the second 110°. We have here a difference of 30°, 
arising solely from the manner in which the instruments were ex-r 
posed. These trials are so few in number, that, were it not for 
the remarkable uniformity of the differences, it might appear 
unreasonable to apply them to any other observations. But it 
cannot be denied, that such a correction would at least render 
Captain Sabine's observations more closely comparable with those 
made at London. So far, then, the hypothesis appears to have 
advanced on trivial grounds. 
In support of his idea, that the energy of the solar rays is 
diminished as we approach the Equator, the narrative of Hum- 
VOL. XIV. NO. 27. JANUARY 1826. 
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