IN PASSING THROUGH THE ATMOSPHERE. 
273 
and to reduce the readings of B. 2. into “ actines ” we have the factor 0*856 X 6*209 
= 5*315. 
The scale of “ actines ” has been added to the margin of the Curve XV. Plate XXII. 
Intensity of extra-atmospheric radiation, 
73°*06 B. 2. (Article 97.) = 388*4 actines. 
After vertical transmission through the atmosphere, 
39°*03 B. 2. = 207*4 actines. 
Residual intensity after an indefinite transmission, 
15*2 B. 2. = 80*8 actines. 
Note B. — On Article 48. 
I have certainly not exaggerated here the difficulties in respect of weather. During 
the summer which has passed since the reading of this paper (1842), I have sedu- 
lously sought the opportunity of making some additional actinometer observations 
amongst the Alps, under the most favourable circumstances. But though the season 
was, as every one knows, more than commonly fine, I did not succeed in getting a 
single series of observations worth preserving, of the kind which I required. Ex- 
cepting about three days in the end of June, and perhaps as many in the middle of 
August, the whole summer presented no unexceptionable weather, and on these two 
occasions I was unavoidably prevented from making use of my instruments, of 
which I had taken two from England on purpose. One experiment which I desired 
to make was, to push the observations to still greater thinness of atmosphere than 
could be obtained at the Faulhorn so late as the month of September, and for this 
purpose I proposed to ascend the Cramont (8966 feet) soon after the summer solstice, 
and I actually did spend a whole day without result on the summit in the month of 
July. By making single observations throughout the greater part of a day, I pro- 
posed to push the experimental Curve XV. further than had yet been done. 
I also proposed another experiment which I recommend to future observers. I 
coated the bulb of one actinometer with white paint. The comparative value of the 
scale of this and another naked or dark blue bulb, would depend upon the nature of 
the incident heat (see Art. 3.). With heat from terrestrial sources transmitted by most 
diathermanous bodies, the colour of the surface becomes more and more influential, 
as the heat has been drained of its more absorbable part. But it would be very in- 
teresting to verify the fact in the case of the solar rays passing through air. For this 
purpose I proposed to compare the white and the dark actinometers at the top and 
at the bottom of a high mountain such as the Cramont, and I expected to find the 
disproportion least above and greatest below. 
2 N 
MDCCCXLII. 
