NEW CLOUD CLASSIFICATIONS. 
79 
southeast instead of from the south, as reported, and the 
upper clouds at Knoxville given as calm were probably 
moving from the east. A stratus cloud at Cincinnati has 
been mistaken for a cirro-stratus. If this much can be done 
without a close and sharp cloud definition, how much could 
have been obtained from cloud observations taken in accord¬ 
ance with the system to be mentioned below ! 
At the International Meteorological Conference held in 
Munich in 1891 the question of improving our cloud nomen¬ 
clature was discussed, and a committee, consisting of Pro¬ 
fessor Hann, Professor Hildebrandsson, Professor Mohn, and 
Messrs. Piggenbach, Potch, and Tiesserence de Bort, was 
appointed to prepare a cloud atlas. At the International 
Conference at Upsala, in 1894, this committee recommended 
the cloud classification of Hildebrandsson, A bercromby, and 
Koppen, adding the word “ diurnal ” to one of the cumulus 
groups. The new international classification thus recognizes 
ten principal forms : 
a. Detached or rounded forms (most frequent in dry 
weather). 
b. Widespread or veil-like forms (wet weather). 
A. Highest clouds; mean height, 9,000 meters: 
a 1, cirrus. 
b 2, cirro-stratus. 
B. Clouds of mean altitude, 3,000 to 7,000 meters : 
a 3, cirro-cumulus. 
4, alto-cumulus. 
h 5, alto-stratus. 
C. Low clouds, 2,000 meters: 
a 6, strato-cumulus. 
b 7, nimbus. 
D. Clouds formed by diurnal ascending currents : 
8, cumulus; top, 1,800 meters; base, 1,400 meters. 
9, cumulo-nimbus ; top, 3,000 to 8,000 meters ; base, 
1,400 meters. 
E. Elevated fog below 1,000 meters. 
10, stratus. 
