28 Experiments and Observations on the Solar Rays. 
Arr. IIl.—Ezperiments and Observations on the Solar Rays ; 
by Epwin C. Leepow, M. D., of Plymouth, Montgomery Co., 
Pennsylvania. 
Tue difference of heat acquired by a white and a black body, 
when both are equally exposed to the sun’s rays, has long attract- 
ed the attention of observers. “If a black and a white glove 
are worn by the same person in the sun, the hand with the black 
glove will acquire the greatest degree of heat. Dr. Watson, the 
present Bishop of Landaff, covered the bulb of a thermometer 
with a black coating of Indian ink, and the mercury presently 
rose 10°. Black clothes heat more and dry sooner in the sun than 
white clothes.”* 
The following experiment was performed by Franx.in. 
‘On a winter’s day when the ground is covered with snow, 
take four pieces of woollen cloth of equal dimensions but of dif- 
ferent colors, black, blue, brown and white, and lay them on the 
surface of the snow in the immediate neighborhood of each oth- 
er. Ina few hours the black cloth will have sunk considerably 
below the surface ; the blue almost as much; the brown evident- 
ly less; and the white will remain precisely in its former situa- 
tion.”’t 
Having described upon a piece of black paper, a circle one fifth 
of an inch in diameter, I condensed the sun’s rays with a lens 
upon the paper, so as just to fill this circle, which quickly pro- 
duced an emission of smoke accompanied by the odor of burn- 
ing paper. The rays were then concentrated upon a piece of 
white and perfectly clean paper, so as just to fill a circle about 
one twentieth of an inch in diameter; but no discoloration of 
the paper, emission of smoke, or any thing indicating an approach 
to combustion, could be observed. Now, it is apparent that the 
condensation of the rays within the smaller circle, must have 
been to that within the larger circle, as the area of the latter to 
that of the former, which, upon computation, will be found to be 
as 16: 1. 
From these experiments it appears that there is a vast differ- 
ence between white and black opaque bodies, as regards the ef- 
* Greg. Dict. of Arts and Sci., Article Black. 
t Webster's Manual Chem. (Henry 105.) 
