TROPICAL AND POLAR ELECTRICITY.

259

metals, and exhibiting the intensity of electric action, similar to the powerful battery of large plates.

But the electro-polar state is widely different; lightning conductors are not needed where lightning is scarcely seen. And in respect to the action of the magnetic needle, there is a curious circumstance stated in the Transactions of the Royal Society," 1738.

Captain Middleton noticed that while among the ice in Hudson's Bay his compasses would not work or traverse, except he heated them by the cabin fire, and then they worked very well, so he always kept one by the fire, and replaced it in the binnacle, changing them every half hour. "

The electricity of the polar circle is quantity, diffused in the upper portions of the atmosphere, and manifesting itself in a quiet, gentle, and innocuous form of the aurora, playing in an elegant and graceful manner for hours together. The lightning is electricity in a concentrated state, and of great intensity. The aurora is quantity, greatly diffused and of low intensity.

Does each tropic and the pole form a battery, and do they influence each other through the medium of electricity ?

During the summer the tropic is incessantly discharging immensity of lightning, and the polar region is quiescent, as far we know of it by the aurora, because the needle does not exhibit the signal of its presence. In the winter the tropic electricity is more quiescent; but the polar exhibitions of the aurora are more frequent and perhaps almost continuous.

260 THE CIRCUIT OF ATMOSPHERIC ELECTRICITY.

Does the aurora discharge in an innocuous manner a large amount of electricity which would otherwise take the lightning form?

From whence comes the electricity of the polar regions? The constant afflux of winds from the warmer regions towards the pole, fraught with moisture-these it is that bring a constant supply of vapour with its latent heat and electricity. The vapour is condensed, precipitated, and sets free its latent heat and attached electricity. The heat and electricity mount upward and soar aloft, and constitute the peculiarity of the polar atmosphere. The S. W. winds, whose course we endeavoured to trace, and observe their conversion into N.W. winds, either rush down with impetuosity, or wend their silent way by an upper current towards the south, and thus return again to the place from whence they came. The electricity attached to the vapour, now disentangled, struggles to get back again, and spreads itself out upon the sky, returning by the upper plane to the regions of its birth. Thus the circuit is completed, and the system of its transfer perfected. The S.W. winds carried it on its wings, and the N. W., with its cirrous expansions, transmit the current back. It goes by the lower road, and returns by the higher.

CHAPTER X.

Definition of Recurring Monthly Periods.—Recurring Solar Periods.—The Rotation of the Sun.-The frequent Monthly Recurrence of 21st day.— Extent of Recurring Monthly Periods.-Gradual Progression from Change. -Tendency to frequent Recurrence of the same Number-Examples of frequent Recurring Numbers.-Diathesis of the Seasons.-Application of Recurring Monthly Periods.-Mode of Application.-Practical Testimony of fifty successive years. -Simultaneous Action of two Areas.-Monthly Periods involve larger Periods.-Drought in the Days of David.-Drought at the Cape de Verdes.-Drought at Buenos Ayres.-Famine in Egypt.Drought of three years in Samaria.-Transfer of Heat, the Locomotive Power.-Barometer affected by the Transfer of Heat.-Periodic System of the Atmospheric Actions.-Nature's Divine Truth, a Hymn.-The Seasons call on Man for Adoration.

CHAPTER X.

By the designation, "Recurring Monthly Periods of Atmospheric Action," it is intended to denote a "mean period of thirty days twelve hours," corresponding very nearly to a solar month, or that space of time in which the sun passes through one sign of the zodiac. There is a variation of two days on either side of the mean, so that we have the following

and so on throughout. Any state or condition of the atmosphere, recurring in succeeding months, within two days of the same time of each other, is included in, and constitutes, a recurring monthly period.

For convenience and propriety, the specific points of highest and lowest state are taken for standard reference and exemplification, and not that they are the only recurring points or conditions. The mean period was deduced from the "Greenwich Observations," in which alone the precise hours of the highest and lowest states are