178 Prof. J. Brockleshy on the Influence of Color on Dew. 
I have thtown out a few ideas suggested by this memoir of M. 
Laurent, and have at the same time pointed out the basis upon 
which it appears to me a true natural system of chemical classi- 
fication can be founded. Imperfect as they are, I hope they may 
not prove unworthy of the consideration of scientific men, and 
tend to forward the progress of chemical —— y: 
= 
* 
Art. XIV.—Upon tie roe of Color on Dew; by Prof. 
n Brocxuessy. 
In those haem Pid ee from which Dr. 
Wells derived his theory of dew, the influence of various mate- 
rial properties, in aetennguins the amount of moisture deposited 
upon bodies, under like exposures, is clearly and satisfactorily un- 
folded. We are however left to regret, that this sagacious ob- 
server did not illustrate the effect of color, by a full course of ex- 
periments. 
This subject indeed was not entirely omitted. In four out of 
five experiments, made with parcels of black and white wool, 
alike in size and weight, he discovéred that the former had gained 
a little more dew than the latter ; but as the fibres of the white 
wool were somewhat coarser than those of the black, he accounts 
for the entire difference in the quantities of moisture from this 
circumstance alone. 
At another time he exposed a piece of pasteboard covered with 
white paper, and close to this a second piece, similar in every re- 
spect to the ae covered with paper blackened with ink. In the 
morning he b held hoar- frost upon both the cards, but the black 
surface saateele to have gained a greater quantity than the white. 
A doubt however rose in the mind of the observer upon. this 
point, inasmuch as from the contrast of color the amount of hoar- 
frost might have been apparently greater‘upon the dark than upon 
the light surface even when no real difference existed* in favor of 
the black. 
Influenced by certain views in regard to the effect of the chem- 
ical constitution of bodies in modifying radiation, Dr. Welles pur- 
sued this inquiry no farther. 
e stibject here rested until the year 1833, when Dr. Stark of ' 
Pdinbaty instituted a series of experiments to determine the in- 
fluence of color upon heat, odors and dew.t Two ie eis 
* This appearance I have egret observed, when the Beato of dew upon 
the white exceeded that oi on the blac 
835, Prof. Bache of the le of a “gin 0 the influ- 
ence of color upon the saad of non-lumineus heat. His experiments were 
hy, 
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