NO. IO REFLECTING POWER OF CLOUDS — ALDRICH 9 



markings Venus is usually regarded as altogether cloudy. If this 

 is the case, unless the clouds are very deeply broken up by pits and 

 billows an albedo for total radiation of 78 per cent (or even a little 

 more considering the specular reflection near the edges of the sunlit 

 surface) would be expected. Young notes that the limb of the 

 planet is always much brighter than the central parts. This may indi- 

 cate that the clouds while general are not thick enough to give full 

 cloud reflection except for rays received obliquely. 



SUMMARY 

 A pyranometer suspended below the basket of an army observation 

 balloon was used to measure the reflecting power of a level cloud sur- 

 face practically filling a hemisphere of solid angle. Over one hun- 

 dred determinations were made. The solar air masses ranged from 

 3.8 to 1.2, and the sky above was cloudless and very clear. A mean 

 value of 78 per cent is obtained. No change of total reflection de- 

 pending on solar zenith distance is apparent within a range of zenith 

 distance from 33 ° to 69°. A value of 43 per cent for the albedo of 

 the earth is obtained by revision of the earlier value of Abbot and 

 Fowle (Annals, Vol. II, p. 162) which depended on a lower value 

 of cloud reflection based on observations over but a small part of a 

 hemisphere. 



