Previous Index Next
Page 228
(previous) (Page 000228) (next)

powerless; the one cannot be warmed, nor the other
melted, by such rays. The cloth is white and the snow is
white, because their confusedly mingled particles and fibres
are incompetent to absorb luminous rays. Whether, then,
the cloth will sink or not depends entirely upon the dark
rays of the sun. N ow the substance which absorbs the
dark rays of the sun with the greatest avidity is ice—or
snow, which is merely ice in powder. A less amount of
heat will be lodged in the cloth than in the surrounding
snow. The cloth must, therefore, act as a shield to the
snow on which it rests; and in consequence of the more
rapid fusion of the exposed snow, the cloth must in due
time be left behind, perched upon an eminence like a gla-

But though the snow transcends the cloth both as a
radiator and absorber, it does not much transcend it.
Cloth is very powerful in both these respects. Let us
now turn our attention to the piece of black cloth, the
texture and fabric of which I assume to be the same as
that of the white. For our object being to compare the
effects of color, we must, in order to study this effect in its
purity, preserve all other conditions constant. Let us then-
suppose the black cloth to be obtained from the dyeing
of the White. The cloth itself, without reference to the
dye, is nearly as good an absorber of heat as the snow
around it. But to the absorption of the dark solar rays
by the undyed cloth is now added the absorption of the
whole of the luminous rays, and this great additional in-
flux of heat is far more than sufficient to turn the balance
in favor of the black cloth. The sum of its actions on the
dark and luminous rays exceeds the action of the snow
on the dark rays alone. Hence the cloth will sink in the
snow, and this is the philos0phy of Franklin’s experi-

Throughout this discourse the main stress has been laid

Previous Index Next