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.
Pages:
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136