Mabch 6, 1914] 



SCIENCE 



343 



5. Atmospheric bands do not exist in the 

 solar spectrum outside the atmosphere. 



6. The quantity of solar energy beyond 

 \ = 0.3fi in the ultra-violet and beyond 

 A. == 3.0 /i in the infra-red is inconsiderable. 



The soundness of these assumptions is 

 best proved by the results of a great num- 

 ber of observations made at sea level and at 

 high altitudes during the last ten years by 

 different observers, but mainly by the staff 

 of the Astrophysical Observatory of the 

 Smithsonian Institution. 



DISCUSSION OP LANGLEY'S SOLAR CONSTANT 

 ViVLUE 



With this preliminary we may perceive 

 why the high solar constant value of Lang- 

 ley ought not to be accepted. For this 

 purpose consider lines 26 to 43 of page 144 

 of the Mount Whitney report, which detail 

 the precise method employed in obtaining 

 what Langley regarded as a minimum 

 value, namely 2.63 calories per square 

 centimeter per minute. 



We now proceed to determiiie from our bolom- 

 eter observations a value which we may believe 

 from considerations analogous to those just pre- 

 sented, 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 trans- 

 missibility increases (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 ft. and which caused a 

 deflection a.t 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 observations 

 at Lone Pine then, the heat of this ray upon the 

 mountain should have been 



201 X 1,000 -i- 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 at- 

 mosphere, calculated from Mountain Camp high 

 and low sun observations (275) by the ratio 

 2497/2060 we have 333.3, where 333.3 represemts 

 the energy in this ray outside the atmosphere as 

 determined by this second process. In like man- 

 ner we proceed to deal with the rays already 

 used, thus forming column 8 in Table 120. 



It is evident that the transmission coeffi- 

 cient determined for the wave-length 0.6 /i 

 by the aid of high and low sun observations 

 at Lone Pine, represented the mean trans- 

 mission 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 transmis- 

 sion 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 layers are least transparent,^ there- 

 fore the value 0.976 could be known, 

 a priori, not to represent the transmission 

 of the air between 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 ob- 

 served 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 com- 

 putation of the intensity at Mountain 

 Camp just quoted with a coefficient p which 

 was certainly wrong. The argument on 

 which Langley acted may be stated in a 

 plausible form as follows: If Bouguer's 

 exponential formula with the transmission 

 coefficient obtained by high and low sun 

 observations at Lone Pine gives too low a 

 value of the intensity of homogeneous solar 

 radiation for a station within the atmos- 

 phere like Mountain Camp, as was shown 

 by actual observation, much more will it 



s See Table 118 of the Mount Whitney Report. 



