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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 70 



Mr. Aldrich, one of the officers went up with the balloon, which 

 carried the pyranometer suspended inverted underneath its basket, 

 and exposed the apparatus repeatedly from about 7 o'clock in the 

 morning until about ii o'clock. The measurements were recorded 

 by Mr. Aldrich on the ground by the aid of communicating wires 

 carrying the currents of electricity set up by the heat of the rays 

 received from the fog upon the instrument. 



The measurements were singularly concordant and satisfactory, 

 and gave as the mean reflecting power of the fog during the interval 

 from 7 until 1 1 o'clock 78 per cent. No apparent change due to 

 the change of the height of the sun during that time was observed. 

 However, it is hardly questionable that if the measurements had been 

 made nearer sunrise the reflecting power of the fog would have been 



Fig. 2"/. — Smithsonian Observatory at Calama, Chile. 



found somewhat greater. Accordingly, we must suppose that if 

 there should be a planet completely covered with smooth clouds it 

 would reflect upwards of 78 per cent of the solar rays otherwise 

 available to heat its surface. In the case of the earth, the cloudiness 

 is about 50 per cent, so that if the clouds were as smooth on their 

 surface as the clouds observed by Mr. Aldrich, the resiflt would be 

 that they would reflect away about 39 per cent of the solar rays and 

 make them ineff^ective to warm the earth. Taking this result in 

 connection with the consideration of the other parts of the earth's 

 surface, it appears that the reflecting power of the earth as a w^hole 

 for solar rays of all wave lengths should be in the neighborhood of 

 43 per cent. 



As stated above, the measurements of the solar radiation at Mount 

 Wilson have unusual value this ^■ear on account of the simultaneous 



