Periodical Literature 101 



are found to lie upon an equilateral hyperbola, and by extrapola- 

 tion values for daylight intensities are obtained. 



The author makes extensive use of the theory of errors in dis- 

 cussing the reliabilities of his results going rather fully into his 

 procedure as is still necessary in writing for foresters, in Germany 

 as here. And here it may be remarked that should there remain 

 any who are unconvinced that the characteristic spirit of modem 

 research consists in the careful observation of quantities chosen 

 with the apparent arbitrariness, the mathematical digestion of the 

 results and the formation of modest conclusions let him read this 

 paper. 



Direct sunlight was not measured as the instrument is too 

 sensitive and all readings were made of diffuse skylight only. 

 Each observation in the forest was checked against a reading in an 

 opening nearby. Readings were made wdth and without a screen 

 of 30 per cent, solution of ferroammonium sulphate which served 

 to exclude practically all of the infra-red rays. 



Under crowns of different densities there are of course differences 

 in the total amount of diffuse radiation, although in heavily thinned 

 stands the sk}dight is found to be as intense as in the open, losses 

 being entirely compensated by reflection. There is also a different 

 spectral distribution of the skylight under crowns of different 

 densities because the infra-red is intercepted more largely than the 

 luminous radiation. Beech appears to intercept much more than 

 spruce of the same density. The intensity of the radiation is the 

 same at all points along the merchantable bole as at the surface 

 of the ground. 



For most perfect disintegration of the leaf litter the crowns of 

 beech should be opened up by the removal of one-third to one- 

 fourth of the volume of the stand, while in spruce only about one- 

 fifth should be removed. 



So too, while greatest volume growth is made in beech after 

 the removal of one-fifth to one-foiurth of the volume, spruce 

 requires the removal of but one-seventh to one-sixth to produce 

 the same result. Thinnings in beech must accordingly remove 

 one-half to two-thirds more material than in spruce in order to 

 produce the same result. 



In closing, the author emphasizes the fact that these measure- 

 ments are as yet incomplete and should be very largely multiplied 



