142 REPORT—1840. 
headed cumulus contrasted with the flaky cirrus—without being 
persuaded of the fact, that clouds are not unorganized assem- 
blages of watery particles in a state of extreme division. 
219. With respect to the fall of rain, by far the most inter- 
esting contribution to this part of meteorology, took its origin 
at the rise of the British Association. Prof. Phillips, by his 
careful experiments on the fall of rain at different elevations at 
York, and his admirable deductions from them, has (I think) 
completely established the cause of the diminished fall of rain, 
as we ascend in the atmosphere (vertically above the soil). M. 
Boisgiraud ainé, of Toulouse*, was, I believe, the first in 
recent times} to maintain that this is due to the gathering of 
the drop as it descends, chiefly in consequence of the cold 
which it possesses, due to the height from which it has fallen, 
and also to the considerable dampness of the atmosphere at 
such times. This, the experiments of Mr. Phillips and Mr. 
Gray entirely confirm, and I think demonstrate f. 
220. For 12 months (1833-34) the fall of rain at York was 
as follows :— 
Height above Ground. Rain in Inches. 
if feet ropes); 2. sai) er ROR 
Ad: ogy acs is Mellen) oo) ORO 
DSO, GixwNoad Giese wile om). Wha aine 
The diminution was, therefore, 41°8 per cent. for 213 feet. 
29 22°8 29 44 5, 
which is pretty nearly as the square root of the height. This 
proportion does not hold for different seasons ; and though the 
formula m 7 height, originally proposed by Mr. Phillips (m 
being a function of the air-temperature), is a tolerable approxi- 
mation, it does not appear to be an accurate one. Nor indeed 
have we any reason to suppose that so simple a law should 
express the effect, on the author’s own hypothesis, since (ad- 
mitting that the rain-drops have attained a terminal velocity) 
the deposition on the drop must involve the size of the drop, 
the dryness of the air, and the decrement of temperature in the 
atmosphere in a very complicated manner §. 
221. Admitting, however, for a moment, Mr. Phillips’s ori- 
* Annales de Chimie, xxxiii. 417. 
+ Prof. Bache, of Philadelphia, has claimed, with reason, for Dr. Franklin, 
the merit of first suggesting the explanation, so far as the imperfect science of 
his time would fairly allow him to do.—Journal, Franklin Institute, vol. xvii. 
1836. 
t British Association, 3rd Report, p. 401; 4th Report, p. 560; 5th Report, 
pel Writ 
§ The optical phenomena of the rainbow, to which we shall presently ad- 
vert, confirm, in a remarkable manner, the increased size of drops in falling. 
—See Arago; Annuaire, 1836, p. 301. 
