consists in the tracing out of this interdependence, and
the demonstration of this harmony. The outward and visible phenomena
are the counters of the intellect; and our science would not be worthy
of its name and fame if it halted at facts, however practically
useful, and neglected the laws which accompany and rule the phenomena.
Let us endeavour, then, to extract from the experiment of Franklin all
that it can yield, calling to our aid the knowledge which our
predecessors have already stored. Let us imagine two pieces of cloth
of the same texture, the one black and the other white, placed upon
sunned snow. Fixing our attention on the white piece, let us enquire
whether there is any reason to expect that it will sink in the snow at
all. There is knowledge at hand which enables us to reply at once in
the negative. There is, on the contrary, reason to expect that, after
a sufficient exposure, the bit of cloth will be found on an eminence
instead of in a hollow; that instead of a depression, we shall have a
relative elevation of the bit of cloth. For, as regards the luminous
rays of the sun, the cloth and the snow are alike 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 fibres
and particles are incompetent to absorb the luminous rays. Whether,
then, the cloth will sink or not depends entirely upon the dark rays
of the sun. Now the substance which absorbs these dark rays with the
greatest avidity is ice,--or snow, which is merely ice in powder.
Hence, a less amounts 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, its shield must, in due time, be left behind,
perched upon an eminence like a glacier-table.

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
colour, we must, in order to study this effect in its purity, preserve
all the 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