636 



5 mm. thick was produced on the trees, the temperature of which in all 

 parts lay under zero. The period of the still frost lasted 5 to 6 days in 

 this Viennese forest ; the ice covering remained 9 days and increased until 

 the thinnest branches grew to the size of a ship's rope; the beech trunks 

 broke, while the young copse wood was bent to the ground. Since only the 

 surface of the soil was frozen, the trees were also overthrown. The 

 needles of the conifers especially favored the formation of ice and firs 

 became ice pyramids, since the icicles, often 20 cm. long on the upper 

 branches, were frozen to the lower branches. 



In low positions, the covering was actually transparent, smooth ice; on 

 the heights, however, the chief part consisted of a mixture of ice and mist. 

 In the same way, the size of the ice particles decreased gradually from the 

 edge of the forest toward the centre, where the covering was neither ice 

 nor mist but had a firm, ray-like consistency, until finally, deep in the forest, 

 it appeared as a typical mist covering, which became thinner and thinner 

 the deeper one penetrated into the forest. In order to form a conception 

 of the amount of ice thus produced, which also occurred simultaneously in 

 Germany and France, the weight of the ice, hanging on a single branch, 

 was determined with the following results : for the one part weight in a 

 leafless cherry branch, the ice was 36.7 parts; in the Zerr oak, 44.1 ; in the 

 red beech, 85.3; in the fir, 31. i ; in the spruce, 51.3; in the pine, 99.0 parts. 



Breitenlohner, in explaining the phenomenon, calls attention to the 

 fact that the observations of meteorological stations, at the time of the ice 

 covering, showed the action of a south wind; therefore, a moist, warm 

 equatorial current above a cold polar stream filled the valleys. The contact 

 of the equatorial with the polar air waves led to the unusual form of precipi- 

 tation. This remained fluid because the lower, cold stream of air was not 

 very thick vertically, so that the precipitation, coming from a warm current, 

 had to pass only a short way through cold air. 



Where the cold layer of air had a greater vertical thickness, the pre- 

 cipitation took on a solid form and covered the vegetation as hoar frost. 



The precipitation, formed after the contact of two layers of air, which 

 differ in temperature and moisture, can retain its consistency as fluid water 

 even below zero degrees, since moist winds are splendid heat producers and 

 carry an amount of latent warmth in water vapor which is freed during the 

 continued condensation. Only when the cooling agent exceeds a certain 

 amount is the mist changed into frost vapor and then the moisture eUm- 

 ination consists of ice needles. The peripheral trees, exposed to the free 

 currents of air, catch and hold the mist, while, in the interior, the choked 

 air causes the formation of the typical mist covering. 



This, therefore, would be analogous to hoar frost, occurring with late 

 or early frosts, and, therefore, cannot be considered to be frozen dew. 

 Dew is condensed water vapor, which is precipitated in drops on the parts 

 of the plant cooled down below the condensation point of the air by radia- 

 tion. These drops unite. Water vapor is usually abundantly present in 



