28 



SMITHSOXIAX MISCELLANEOUS COLLECTION: 



VOL. 70 



Mr. Aldrich. one of the officers went u]) with the Ijalloon. which 

 carried the pvranometer suspended inverterl underneath its Ijasket. 

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

 morninij until about 1 1 o'clock. The measurements were recorder! 

 Ijv Mr. Aldrich on the ,L;"round by the aid of communicating' wires 

 carrying the currents of electricity set u]) Ijy the heat of the rays 

 received from the fog upon the instrument. 



The measurements were singularl_\- concordant and satisfactory. 

 and gave as the mean retiecting- power of the fog during the interval 

 from 7 until 1 1 o'clock 78 per cent. Xo ap]jarent 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 Ob.se-rvatory at Calama, Chile. 



foimd somewhat greater. Accordingly, we must suppose that if 

 there should be a planet completed- covered with smooth clottds it 

 woukl 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 tl:at if the clouds were as smooth on their 

 surface as the clouds observefl b_\- Mr. Aldrich. the result would be 

 that the\" would reflect away about 39 ])er cent of the solar ra}-s and 

 make them ineft"ective to warm the earth. Taking this result in 

 connection with the consideration of the other ]jarts of the earth's 

 surface, it appears that the reflecting ]jower of the earth as a whole 

 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 unu^ual value this vear on account of the simultaneous 



