Prof. Langley, in this theater, in a
remarkable and interesting lecture, in which he described his journey up
Mount Whitney to about 12,000 feet, told us that the sun was really blue
outside our atmosphere, and at first blush the amount of extra blue which
he deduced to be present in it would, he thought, make it so. But though
he surmised the result from experiments made with rotating disks of
colored paper, he did not, I think, try the method of using pure colors,
and consequently, I believe, slightly exaggerated the blueness which
would result.
I have taken Prof. Langley's calculations of the increase of intensity
for the different rays, which I may say do not quite agree with mine, and
I have prepared a mask which I can place in the spectrum, giving the
different proportions of each ray as calculated by him, and this when
placed in front of the spectrum will show you that the real color of
sunlight outside the atmosphere, as calculated by Langley, can scarcely
be called bluish. Alongside I place a patch of light which 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.
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