404 KANSAS CITY REVIEW OF SCIENCE. 
There are seven distinct varieties of clouds, arranged in two groups, known as 
primary and secondary. ‘The primary group embraces the varieties called cumu- 
lus, stratus, cirrus, and nimbus ; the secondary, the forms designated cirro-cumu- 
lus, cirro-stratus and cumulo-stratus. This classification is quite faulty, as the 
words primary and secondary are not used in their true meaning. The word 
primary signifies pertaining to the first, hence primary clouds ought to mean the 
original or first forms of clouds—those forms which they assume at the beginning 
of their existence. Now, of the four varieties styled ‘‘przmary clouds,” but two, 
the stratus and the cumulus, can properly be called primary, as they only are 
original forms. A better classification is as follows: 
( Primary a. Stratus. 
Te or 
Original. 6. Cumulus. 
CLoups. 4 ( ¢. Cumulo-stratus. 
Secondary | @. Nimbus. 
JUNE or e. Cirro-stratus. 
Transformed. | / Cirro-cumulus. 
i ee @ireus: 
The processes of cloud formation and transformation are easily understood 
if we are sufficiently observing. ‘The manner in which primary clouds originate 
has been briefly stated already, or rather that part of the subject relative to the 
formation of the cumuli—an interesting phenomenon which may be witnessed 
during the forenoon of almost any day insummer. ‘The name, stratus, is applied 
to that form of cloud which often floats near the surface of the earth after a 
heavy rain-storm, also to those with which, in autumn and winter the entire hea- 
vens are often obscured. A third though less common form of the stratus is 
sometimes seen during the evening of the cooler days of summer, and is caused 
by the settling of cumuli to lower strata of air. The lower portion of a cloud 
when approaching the earth in this manner, is usually changed to invisible vapor, 
the air which it enters being warmer and consequently more capable of holding 
moisture. ‘The rounded or conical form of the cumulus is by this means made 
to resemble the stratus, and after a short time, a perfect form of the latter will be 
produced by lateral expansion caused by gravity. This form of the stratus is 
short-lived, never being converted into any other kind of cloud—but is soon dis- 
sipated into invisible vapor. That form of the stratus which is often seen just 
after a heavy rain (particularly if the latter be followed by a strong east or south- 
east wind), is produced when the lower stratum of air is, in its parts nearest the 
earth’s surface, too warm to be in a saturated condition, while at an elevation of a 
few hundred yards the temperature is so low as to cause the vapor to condense, 
When this phenomenon occurs there are usually two strata of clouds, one moving) 
diametrically opposite or at right angles to the other. This form of the stratus 1 
an original cloud while that previously described isa modification of the cumulus, 
The direction taken by these clouds, is dne of the best of weather indicators. 
