Page:Popular Science Monthly Volume 86.djvu/133

Rh that the influence of the moon, the planets and the stars (not including the sun) is practically nil, when terrestrial weather is considered. It should be remembered, in this connection, that heat is the fundamental force determining weather—the form of energy outweighing all others combined. When it is stated that the sum total of all the heat energy received from all heavenly bodies (not including the sun) is so slight that one of the most delicate of instruments is required for its measurement, it is apparent that their influence upon our weather is negligible. The moon, about which most misconceptions of this character center, is without doubt the direct cause of ocean and atmospheric tides, and there are places along certain coasts where ocean tides produce periodic tidal breezes. Aside from the indirect effects here enumerated astronomical influence upon weather is practically of no consequence. The untruth of the proverb which states that the moon tends to drive away the clouds is explained partly by the fact that a clearing of the sky at night is not ordinarily observed unless the moon is above the horizon, and partly by the fact that after sunset there is a cessation of the ascending currents which result in the formation of clouds of the cumulus type, the clouds already formed soon dissipating.

Contrary to a fairly general impression, there is no apparent relation between earthquakes and the weather. Scriptural allusions to destruction of life and property often associate earthquakes and violent storms as though they were of common origin, and the idea has persisted, to some extent, even in modern writings. In general, it may be said that earthquakes are caused by forces at work within the earth, or at least beneath its surface, such as the slipping of the crust along a fault plane, or the movement of molten matter or steam beneath the hard crust. On the other hand, weather changes result from the effects of forces at work within the atmosphere itself, primarily as a product of energy coming through space from the sun. Various investigators have attempted to discover a relation between barometric pressure of the atmosphere, earth tides and local disturbances of the crust. Aside from this possible indirect relationship there is no Imown coordination of earthquakes and the weather.

Nor is there any marked relation between magnetic phenomena and the weather. Magnetic storms, or disturbances in the magnetic state of the earth, frequently occur without any apparent effect upon the weather. That there is a relation between magnetic phenomena in the earth, auroras, and solar disturbances, particularly sunspots, there can no longer be any doubt. The aurora borealis, seen in northern latitudes, and the aurora australis, seen in southern latitudes, are believed to be caused by electrical discharges in the rarefied strata of the earth's upper atmosphere. Aside from the visible manifestations of such discharges, observers have sometimes noticed sounds, and, upon rare occasions, odors