ch is very
closely the color of sunlight on a July day at noon in England. This
comparison will enable you to gauge the blueness, and you will see that
it is not very blue, and, in fact, not bluer perceptibly than that we
have at the Riffel, the color of the sunlight at which place I show in a
similar way. I have also prepared some screens to show you the value of
sunlight after passing through five and ten atmospheres. On an ordinary
clear day you will see what a yellowness there is in the color. It seems
that after a certain amount of blue is present in white light, the
addition of more makes but little difference in the tint. But these last
patches show that the light which passes through the atmosphere when it
is feebly charged with particles does not induce the red of the sun as
seen through a fog. It only requires more suspended particles in any
thickness to induce it.

In observations made at the Riffel, and at 14,000 feet, I have found that
it is possible to see far into the ultra-violet, and to distinguish and
measure lines in the sun's spectrum which can ordinarily only be seen by
the aid of a fluorescent eye piece or by means of photography.
Circumstantial evidence tends to show that the burning of the skin, which
always takes place in these high altitudes in sunlight, is due to the
great increase in the ultra-violet rays. It may be remarked that the same
kind of burning is effected by the electric arc light, which is known to
be very rich in these rays.

Again, to use a homely phrase, "You cannot eat your cake and have it."
You cannot have a large quantity of blue rays present in your direct
sunlight and have a luminous blue sky. The latter must always be light
scattered from the former. Now, in the high Alps you have, on clear day,
a deep blue-black sky, very different indeed from the blue sky of Italy
or of England; and as it is the sky which is the chief agent in lighting
up the shadows, not only in those regions do we have dark shadows on
account of no intervening--what I will call--mist, but because the sky
itself is so little luminous. In an artistic point of view this is
important. The warmth of an English landscape in sunlight is due to the
highest lights being yellowish, and to the shadows being bluish from the
sky light illuminating them. In the high Alps the high lights are colder,
being bluer, and the shadows are dark, and chiefly illuminated by
reflected direct sunlight. Those who have traveled