84 
MC ADIE. 
but confined to the edges, we have billow clouds; but while 
mixture is the most common cause of cloud formation, the 
cloud thus formed is not apt to give heavy rain. Clouds 
formed under the third heading (ascension), on the contrary, 
do give heavy rains. Here the cooling is by adiabatic ex¬ 
pansion, and the ideal type of this formation is the cloud of 
the early afternoon in the tropics, with its torrential rain. 
Under the fourth heading (electrical) the cloud may keep 
adding to itself because of a very high surface electrification, 
or a cloud may be in such a critical condition that, as said 
above, the slightest jar suffices to produce great change. It 
is conceivable that a cloud burst may be a sudden change 
of condition. 
A classification by origin and level gets rid of the confus¬ 
ing “ alto,” or lower, which is still retained—unfortunately, 
we think—in the international classification. This is such 
a handy word that it is liable to be overworked. Thus in 
the first of the following classifications we have “ high alto¬ 
cumulus” and “ low alto-cumulus.” 
Classification of Clouds according to Prof. W. M. Davis ; Elementary Meteoro- 
logy, p. 179 (Blue Hill, Mass, values). 
12 Types. 
Kind of cloud. 
Summer 
height. 
Winter 
height. 
Cirrus ... 
m. 
9,923 
8,754 
6,481 
7,606 
6,406 
3,168 
2,003 
8,242 
m. 
8,051 
7,846 
2,930 
6,992 
Hio'h cirro-stratus ... 
Low cirro-stratus. 
Cirro-cumulus... 
High alto-cumulus. 
Low alto-cumulus... 
2,884 
Strato-cumulus ... 
11 False cirrus ”... 
Cumulo-nimbus. 
Cumulo-nimbus (base)... 
1,202 
2,181 
1,473 
712 
583 
1,552 
Cumulus (top)... 
Cumulus (base).. . . 
1,381 
Nimbus. 
Stratus.„... 
503 
