322 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



geneous, that is to say, monochromatic rays. He was thus led to 

 fix the solar constant at 3 calories per square centimeter per minute, 

 which now appears to be fully three halves the true value. I quote 

 his own words in description of the method by which this value was 

 derived : 



We now proceed to determine from our bolometer observations a value whicb 

 we may believe * * * to be a minimum of the " solar constant," and one 

 within the probable truth. All the evidence we possess shows * * * that 

 the atmospbere grows more transmissible as we ascend, or that for equal 

 weights of air the transmissibility increases (and probably continuously) as we 

 go up higher. In finding our minimum value we proceed as follows, still deal- 

 ing with rays which are as approximately homogeneous as we can experiment- 

 ally obtain them. Let us take one of tbese rays as an example, and let it be the 

 one whose wave length is 0.0^, and which caused a deflection at Lone Pine of 

 201. The coefficient of transmission of this ray, as determined by high and 

 low sun at Lone Pine and referred to the vertical air mass between Lone 

 Pine and Mountain Camp, is 0.9TG. From the observations at Lone Pine, then, 

 the heat of this ray upon the mountain should have been 



201 X«=« =206.0, 



but the heat in this ray actually observed on the mountain was 249.7. There- 

 fore, multiplying the value for the energy of this ray outside the atmosphere 

 calculated from Mountain Camp high and low sun observations (275) by the 



ratio ^—, we have 333.3, where 333.3 represents the energy in this ray out- 

 side the atmosphere as determined by this second process. 



By this process Langley obtained the solar-constant value 2.630 

 calories, which he considered a minimum. By another process he 

 obtained the value 3.505, which he considered a maximum. The 

 mean of the two he chose as the solar constant, or, in round numbers, 

 3 calories. 



Langley's argument is, of course, that if we find our formula giv- 

 ing too small values at a station within the atmosphere to which we 

 can ascend, probably it would give values even smaller in proportion 

 to the true one outside the atmosphere altogether where we can not 

 go to test it. But in fact the transmission coefficient found at Lone 

 Pine was not applicable to compute what ought to have been ob- 

 served at Mountain Camp. It was applicable to the average trans- 

 missibility of all the layers of the air from Lone Pine to the limit 

 of the atmosphere. It was therefore far too high to suit the trans- 

 mission of the dusty, opaque layers next the earth's surface. Hence, 

 by its use Langley computed a smaller value for Mountain Camp 

 than he observed, but this had really no bearing on the problem. It 

 would seem that the true result to be selected as representing Lang- 

 ley's experiments is the mean of 2.06 found by the unmodified 

 method of homogeneous rays at Lone Pine and 2.22 found in the 

 same way at Mountain Camp. That mean is 2.14 calories. 



