The luminosity of the spectrum observed at the Riffel I
have used as my standard luminosity, and compared all others with it. The
result for four days you see in the diagram.
I have diagrammatically shown the amount of different colors which
penetrated on the same days, taking the Riffel as ten. It will be seen
that on December 23 we have really very little violet and less than half
the green, although we have four fifths of the red.
The next diagram before you shows the minimum loss of light which I have
observed for different air thicknesses. On the top we have the calculated
intensities of the different rays outside our atmosphere. Thus we have
that through one atmosphere, and two, three, and four. And you will see
what enormous absorption there is in the blue end at four atmospheres.
The areas of these curves, which give the total luminosity of the light,
are 761, 662, 577, 503, and 439; and if observed as astronomers observe
the absorption of light, by means of stellar observations, they would
have had the values, 761, 664, 578, 504, and 439--a very close
approximation one to the other.
Next notice in the diagram that the top of the curve gradually inclines
to go to the red end of the spectrum as you get the light transmitted
through more and more air, and I should like to show you that this is the
case in a laboratory experiment.
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