Page:Popular Science Monthly Volume 9.djvu/323

Rh will be condensed into masses of cumulus clouds banked up against the top of the cold current, and arranged over the horizontal stratus clouds. Thus is produced the combination of cumulo-stratus cloud, as represented in Fig. 4, and which is characteristic of progressive summer storms.



To the tornado-cloud produced by a whirl of air, and resembling an inverted cone, Prof. Blasius gives the name of conus, which is both distinctive and appropriate.

These four typical classes of clouds—viz., cumulus, stratus, cumulo-stratus, and conus—indicate and characterize the four different classes of storms.

—With the foregoing facts and classifications in view, Prof. Blasius's method of predicting the approach of storms, "by their embodiments the clouds," can be verified by any careful observer of ordinary intelligence.

—When in winter, while the wind is blowing from the north, thin, hazy bands or stripes of stratus clouds appear low in the southern horizon, it indicates that the warm current from the south is flowing northward, sloping over the polar current, and that the condensation of its vapor into clouds, by successive undulations, has commenced in the upper and colder regions of contact. More and more of these stratus clouds gradually appear, until they cover the entire southern sky and reach the zenith. This may require