DISCUSSION 157 
of rain compared to these small differences im 
space. I may also say that we are now going to 
have a much denser network around Uppsala 
than the one I showed you. 
Dr. C. W. Newton—The hills around Stock- 
holm are about the same as those near Uppsala, 
40 to 100 m in height. While we were in Stock- 
holm, F. H. Ludlam made time lapse movies of 
cloud formations and we were very much im- 
pressed when we noted that Altocumulus clouds 
were very strongly influenced by these 40-m 
hills. I wonder if, even with such low hills, ordi- 
nary orographie lifting can be ruled out. 
Dr. Bergeron—I did not mean to rule out that 
kind of lifting which goes on the theory of lee 
waves, observable at heights surpassing that 
of the obstacles by a factor of 10 to 20, as we 
know. I did allow for that first of all, and 
secondly on an obstacle with forest, 40 m high, 
friction would perhaps increase the effective 
height. I did consider those two things, but I am 
very thankful for the remark. 
