92 Forestry Quarterly. 



Prof. Ramaiin has constructed a photometer 

 Light in which the fact is utilized that the electric 



Measurements conductivity of the metal selenium is increas- 

 in ed by increase of light intensity. The author 



Sprutce admits that for the higher and lower light 



intensities the apparatus may not be reliable, 

 but for low and medium intensities, which are those mostly con- 

 cerned in practical work, he has found it to all intents and pur- 

 poses satisfactory. The description of the instrument and of a 

 series of test measurements is promised for a later date. 



The light intensity for a given area is called lux, i. e., the 

 amount of light which one square centimeter area receives from 

 a normal candle at one meter distance; a lamp of 15-40 candle 

 power at un distance furnishes 15 to 40 lux. As very low degrees 

 of light are ranged those of 150 to 200 lux; as low, 250-300 lux; 

 as medium, 450-550 lux; higher degrees could not be measured 

 with the apparatus. 



In the forest the influence of low degrees is very noticeable, 

 much less so the higher degrees. The illumination in the forest 

 changes continually, light and shade vary with the position of the 

 sun and give rise to the fascinating play of "sunspots." Measure- 

 ments of the light degrees of these sunspots of various size 

 developed that there was more difference than had hitherto been 

 believed, and that the idea that their intensity did not deviate much 

 from that of the general light intensity and had no meaning for 

 the forest floor is a mistaken one. A number of measurements are 

 given, e. g., 60-80 year oak stand, showed a light intensity in the 

 shade of the stand, measured in dili'erent places of 140-1 50-168 

 lux; in sunspots 168-179-225-245 lux. 



After pointing out that the light rays are always accompanied 

 by heat and admitting that, on account of the constant change of 

 sunspots, locally the influence is only small, the author suggests 

 that the total effect must nevertheless be considerable and im- 

 parts to the forest soil characteristics with reference to plant life 

 different from the open. 



The measurements were made from May to August on days of 

 even cloudiness, when light intensities between 9 A. M. and 4 

 to 5 P. M. do not vary very much. 



