abbot: solar constant of radiation 101 



values of E, Eo, a, and m for one station, what would be the 

 value of E at some station of different barometric pressure. ^ 



From this we see that the unit of air mass to be taken for 

 each station is the air mass traversed by beams from zenith 

 celestial objects between the station itself and the outer limit of the 

 atmosphere, not from sea-level. 



The determination of the solar constant of radiation, based 

 upon the demonstration which has just been given, depends upon 

 the following assumptions: 



1. In a homogeneous medium, a homogeneous ray loses a 

 fixed proportion of its intensity in every equal length of its path. 



2. The earth's atmosphere may be considered as made up of 

 a great number of layers concentric with the earth, each approxi- 

 mately homogeneous in itself over the area swept through by 

 the solar beam between zenith distances of 70° and 30° during 

 the time required for this sweep of the beam. 



3. Surface reflection of the outer boundary of the atmosphere, 

 or the boundaries of its internal layers, is negligible. 



4. Except in the known red and infra-red atmospheric bands, 

 the transparency varies gradually from wave length to waye 

 length, or if atmospheric absorption lines exist, the energy they 

 absorb is inconsiderable. 



5. Atmospheric bands do not exist in the solar spectrum out- 

 side the atmosphere. 



6. The quantity of solar energy beyond X = 0.3;u in the ultra- 

 violet and beyond X = 3.0^ in the infra-red is inconsiderable. 



The soundness of these assumptions is best proved by the 

 results of a great number 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 of La7igley's solar constant value. We may now per- 

 ceive why the high solar constant value of Langley ought not to 

 be accepted. For, consider lines 26 to 43 of page 144 of the 

 Mount AYhitney report, which detail the precise method em- 



^ This demonstration applies only to homogeneous rays. 



