246 



masses are constantly set in motion and come to strand on the terraces, 

 etc., thus rediiciDg the danger. 



Some special conditions for the formation of slides exist, when days 

 with a temperature above freezing which thaws the surface of the snow, 

 alternate with cold nights when the surface freezes together. If fresh 

 snow falls on such a surface, it is most liable to form into an avalanche, 

 and sometimes if a heavy snow-fall occurs, it may break through the 

 crust and carr^' the lower masses with it. This hind of slide occurs 

 mostly on southern exposures. 



As regards season and i^eriodicity of slides the greatest diversity ex- 

 ists. I^ew tracks are opened, every year, while in other places the old 

 tracks become scenes of disaster in varying iutervals, some yearly, 

 some every half or every full century. It dei)ends of course on the 

 amount of snow fallen, in connection with weather conditions, espe- 

 cially the direction and force of winds. The most regular faWs occur in 

 spring during time of thaws. 



In wind-still weather and warm sunshine, the time of fall occurs in 

 the first luours of the afternoon, yet if a warm wind blows any time of 

 day or night, the avalanches may start. 



PROGRESS OF AVALANCHES. 



The ground-slides follow more or less the contour of the ground, like 

 running water. Usually the masses start sliding, later on they roll 

 over when passing over steeper and rocky ground, and in rills and fim- 

 nels they are compressed and compacted. 



As in a stream of water, the greatest velocity lies in the center of 

 the slide, where iu a straight track the largest mass and the least fric- 

 tion exists. If turned from the straight track the force is greatest on 

 tlie outer curve, where trees, turf, soil, and rocks are torn up and swept 

 away together. 



Dust-slides occur most frequentl}" during snow-falls at low tempera- 

 tures, especially in windy weather. They occur ofteuer in clear weather 

 than when the sky is clouded. 



RESCUE OF PERSONS BURIED BY AVALANCHES. 



After pointing out the different localities which are exposed to ava- 

 lanches in the Alps, and giving an account of some special cases of dis- 

 asters, which forms most interesting and instructive reading, a chap- 

 ter is devoted to the measures to be taken in saving men lost in snow- 

 slides. The procedure is somewhat like the following : , 



First look over the surface of the snow, where the slide has come to 

 rest, after signs of the unfortunate victims. If no parts of the body are 

 visible outside, determine, according to the location and the track which 

 the slide took, the place where most probably the entombed lie. Then 

 let the rescuers take position in line, and with the handles of shovels, 



