NO. 9 SOLAR ECLIPSE I918 — ALDRICH 7 



not, I believe, be put on a sound basis until an instrument for nocturnal radia- 

 tion is perfected which employs as the radiating and absorbing member a 

 hollow chamber, or so-called " absolutely black body." I believe the dis- 

 crepancy above mentioned results from the facts that both the radiation and 

 absorption of the sensitive strips of the pyranometer and pyrgeometer, and the 

 radiation and absorption of the terrestrial atmosphere differ widely from being 

 " perfect " for wave lengths exceeding 10 microns. 



The reader should not infer that it is admitted that the scale of the pyrano- 

 meter for daylight measurements with glass on is doubtful. Sunbeams and 

 the brightness of the sky embrace rays almost wholly transmissible by glass, 

 and for which the absorption of lamp black paint is well known. Furthermore, 

 as a check to its computed constant the pyranometer with glass on is calibrated 

 against the pyrheliometer. 



In Tables iA and iB are summarized the observations of June 8 

 and June 9. Columns 2 and 3 give the calories of radiant energy 

 reaching" a square centimeter of horizontal surface per minute from 

 the whole sky (the sun being shaded), and from the total sky and 

 sun, respectively. Table iC, showing the brightness of the sky for 

 a typical Mt. Wilson day made with the same pyranometer, is added 

 for comparison. Table iA also gives the values of the outgoing- 

 radiation to space during totality and at night. 



Tables 2A and 2B give values of the air mass and corresponding- 

 solar radiation in calories per square centimeter of surface normal 

 to the radiation per minute all during the eclipse of June 8, and on 

 the afternoon of June 9. These values are obtained by subtracting 

 the total sky brightness from the total sun and sky brightness and 

 dividing by the cosine of the zenith distance of the sun. Table 2C, 

 giving similar values (obtained by pyrheliometry) for a typical Mt. 

 Wilson day, is added for comparison. 



