ways, and that the fundamental cloud-structures which we have just exhibited represent the result of these different conditions.
The varieties of cloud-form and the mixture of structures are of course infinite, but still the delicate fibrous or hairy clouds, the lovely white fleeces on the blue sky, the mountainous rocky masses, and the curious drooping festoons of cloud, are all only the products of condensation under different circumstances.
The result of all modern research leads to the general conception that we live below a sea of air mixed with watery vapour; and that the earth has a coating of that physical manifestation which is called electricity. This atmosphere is in a state of perpetual eddying, and occasionally some of this vaporous air is driven up into such cold high regions that the water is condensed, and the resulting cloud torn and rolled between conflicting currents. Sometimes the electrical coating is so disturbed that equilibrium can only be attained by the disruptive discharge of lightning.
Meteorologists have classified the different kinds of atmospheric eddies; the names of cylones and anti-cyclones will be familiar to you all; and it is found that every different kind of eddy has a different cloud- structure associated with itself.
The motive power for all this is of course the general circulation of the atmosphere, which may either develope great cyclones; small thunderstorms which do not affect the barometer; or that peculiar long roll-like formation associated with what are called "line-thunder-storms."[1]
Socrates and some other of the Greek philosophers seem to have had a suspicion that thunderstorms were of an eddying nature, but they arrived at this conclusion rather by guesswork than by observation. We know it for certain now, as the result of laborious observation on the surface and high-level winds which surround a thunderstorm. For instance, Aristophanes, in the play we have before quoted, introduces the following dialogue:—
"Strepsiades. Tell me, who is it that thunders? This makes me tremble.
- ↑ Full details of these processes are given in the Author's book, Weather, International Scientific Series, No. 59.
