NO. 4 THE BRIGHTNESS OF THE SKY MOORE AND AJJIiOT 



3[ 



1 Sky nearly overcast. Sun appearing only occasionally during morning. 

 "There followed seven readings which showed a very rapid decrease of radiation. 

 ^ Direct sun on instrument. 



Referring to the column of Ratios in the table above, we find a 

 slight increase at a between September 12 and October 2. This is to 

 be expected, for in this place the light was obstructed by high leaves, 

 and many of these had fallen. For place b we find approximately 

 the same ratio for both days, perhaps because the foliage of the 

 saplings and undergrowth did not fall so early as that of the larger 

 trees. The decrease in the ratio at c would follow an increase in 

 the thickness of the ferns. At e, under saplings similar to those of 

 b, a noticeable increase in the ratio occurred. This was very likely 

 due to the absence of any shading by higher trees. 



The results of these observations are meager, and of small re- 

 liability. Nevertheless, they suggest a field for wide and important 

 research, concerning the necessary amount of light for various types 

 of plants and at various stages in their development. The pyran- 

 ometer, supplied perhaps with special colored screens for measuring 

 different kinds of light, seems remarkably well suited to this pur- 

 pose. It is hoped that a much more extensive investigation along 

 this line may be undertaken. 



SNOW OBSERVATIONS 



Late in February, 1918, observations were taken to determine the 

 reflecting power of snow. P^rt of the snow Avas gone at this time, 

 as practically none had fallen since the first of the month, and there 

 had been considerable rain. A suitable patch of snow was found, 

 however, lying on a hillside sloping toward the northeast, not far 

 from the observatory. 



The procedure was as follows : The pyranometer, supplied with 

 glass and thimble of 60° aperture, was mounted on an office stool and 

 box, about four feet above the snow, and in such a manner that it 

 could be alternately pointed at the sky and at such a point on the 

 snow that the direct light and reflected light came from the same 



