324 
growth caused by sublimation, I wonder whether 
from an examination of the frozen center of hail 
stones one could differentiate these processes. 
Mr. List—I think I can answer that last ques- 
tion, but not in an absolute manner. Since our 
institute lies S000 ft above sea level, we can ob- 
serve these graupel stages 20 to 30 times a year. 
We find not many graupel with what is prob- 
DISCUSSION 
ably a frozen droplet in the center, but in about 
40 or 50% we are sure that the center is an 
originating snow crystal. I would say it is not 
necessary to have frozen droplets. 
Dr. Helmut Weickmann—How much did the 
tunnel cost ? 
Prof. R. Sdnger—It cost about 600,000 Swiss 
franes or $200,000. 
