CLOUDS, 405 
If, after a storm, they move foward the north-west, another storm is almost sure 
to follow. This circumstance generally indicates a large area of ‘‘low barome- 
ter,” the center of which is still to the westward of the place of observation, If 
on the contrary, these stratus clouds move /vom the west or north-west, it indi- 
cates rising barometer, fair weather and lowering of temperature. It takes com- 
paratively little experience in weather observation, for one to foretell the weather 
with tolerable accuracy whenever these clouds appear. ‘The stratus is never trans- 
formed into the nimbus as some meteorologists have supposed. It is true that 
mist sometimes falls from these clouds, but even then there is so wide a difference 
between them and true rain-clouds—both in form and origin—that it appears un- 
scientific to consider them rain-clouds. One reason why some have supposed 
that these forms yield rain or are transformed into rain-clouds, is doubtless due to 
the fact that the heavens being sometimes over-spread with them, rain begins to 
fall and continues to do so for a considerable time and in large quantities. The 
truth is simply this—the stratus floats low and obscures the storm-cloud which is 
at a much greater altitude. The rain falls chrowgh the stratus; not from it—the 
rain-drops beginning their descent from points varying in elevation from two to ten 
times that of the base of the lower (stratus) cloud. This feature was particularly 
noticeable on the occasion of the great storm which passed over large portions of 
Iowa and Illinois on July 1st 1878. 
The stratus more than any other form of cloud, has the power of absorbing 
light, or in other words it is a poor reflector. For this reason it always has a 
dark color, though its base is usually less dark than that of the cumulus. It is 
more uniform in color than the cumulus, while its edges are less sharply defined 
both of which facts are due to the difference in their densities. 
Let us now consider the cumulus. This is truly the cloud of day, its typical 
form never appearing in our latitude in the night, unless the weather is very warm 
for the season. The word cumulus, signifies a heap, and is therefore definitive; 
giving a very good idea of the form of the cloud. These clouds are formed 
chiefly during the forenoon of warm days of spring and summer by the conden- 
sation of the vapor contained in ascending currents of air. They attain their 
greatest height during the hottest portions of the day; at which time according to 
Flammarion, they are 10,000 feet above the surface of the earth. In fair weather 
their thickness is rarely more than 2,000 feet, though no figures can be given as 
even approximately correct at a/ times; for latitude and temperature greatly 
modify both their dimensions and their Hiveade. 
; The cumulus, proper, is always an original cloud, by which is meant one 
formed directly from invisible vapor. Its base has a dark or black color, but the 
portions illuminated by the sun are of a beautiful white, sometimes changing toa 
yellowish or ruddy tint—to the former when there is much moisture in the inter- 
vening air, and to the latter when the air is filled with smoke or the so- -called dry- 
og, characteristic of Indian summer. No cloud possesses more beauty than this 
