102 abbot: solar constant of radiation 



ployed in obtaining what Langley regarded as a minimum value, 

 namely 2,63 calories per square centimeter per minute: 



We now proceed to determine from our bolometer observations, 

 a value which we may believe from considerations analogous to 

 those just presented, to be a minimum of the solar constant, and 

 one within the probable truth. All the evidence we possess shows, as 

 we have already stated, that the atmosphere grows more transmissible 

 as we ascend, or that for equal weights of air the transmissibility in- 

 creases (and probably continuously), as we go up higher. In finding 

 our minimum value we proceed as follows, still dealing with rays which 

 are as approximately homogeneous as we can experimentally obtain 

 them. Let us take one of these rays as an example, and let it be one 

 whose wave length is 0.6^1 and which caused a deflection at Lone Pine 

 of 201. The coefficient of transmission for 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 0.976. From the observa- 

 tions at Lone Pine then, the heat of this ray upon the mountain should 

 have been 201 X lOCO ^ 976 = 206.0, but the heat in this ray actually 

 observed on the mountain was 249.7, therefore 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 

 Mtf^ we have 333.3, where .'33.3 represents the energy in this ray out- 

 side the atmosphere as determined by this second process. In like 

 manner we proceed to deal with the ravs already used, thus forming 

 column 8 in Talkie 120. 



It is evident that the transmission coefficient determined for 

 the wave length 0.6/i by the aid of high and low sun observations 

 at Lone Pine, represented the mean transmission of a ray of this 

 wave length through a mass of air containing all the kinds of 

 strata between Lone Pine and the limit of the atmosphere. Such 

 a transmission coefficient would certainly be greater than that 

 which would have been found if the air had all been like that 

 between Lone Pine and Mountain Camp, because the lower lay- 

 ers are least transparent.^ Therefore the value 0.976 could be 

 known, a priori^ not to represent the transmission of the air be- 

 tween Lone Pine and Mountain Camp, but to be certainly greater 

 than the true transmission coefficient for the air between these 

 stations. Accordingly the discrepancy between the computed 

 and observed intensities at Mountain Camp is only what should 

 be expected, and implies no failure of the formula of Bouguer 

 at all; for that formula was used in the computation of the 



< See Table 118 of the Mount Whitney report. 



