One, and the principal end attained by the power of the agent, is the gathering of a volume of atmosphere from, or near, the _surface_ of the land and sea, so as to ensure its possession of all the moisture of evaporation which rises from the locality, and the highest degree of temperature, and from a space ranging from one to two thousand miles in width, in one hemisphere, and to carry it over into the other. Not over the top, or upon the top, of the whole mass of atmosphere situated in the opposite hemisphere--_out of reach of all influences from the earth_--but through it, and curving gradually down near to, and within influential distance of the surface of the earth, soon after it passes the outward limit of its fellow trade; and to continue the current onward, leaving portions of it and its heat and moisture on the way, but taking a considerable volume up and around the magnetic poles--it being impossible for the entire volume to be thus carried around the poles in consequence of the diminished circumference of the earth. To this end it is obvious it must possess _polarity_. Another end to be attained is to combine the moisture of evaporation with the air, so that the cold atmosphere through which, or the earth over which it passes, may not be _continually condensing its moisture_, and thereby _enveloping the earth in a perpetual mist_; but so that it may part with it at _intervals_, making _cloudy_ and _clear days_; and part with it in _portions_, so that a _regular_ and _necessary supply_ may be furnished to the _entire hemisphere_, even up to the geographical poles. Is there such an agent? There is, precisely and perfectly adapted to the ends to be attained, ever there and ever active, and that agent is _magnetism_. [Illustration: Fig. 12.] The earth is a magnet. It has its magnetic poles, and they are distinct from its geographical ones; and there are two in each hemisphere. They are situated from 17 deg. to 19 deg. distant from the geographical poles; and ours is not far from longitude 97 deg. W. from Greenwich, and 71 deg. north latitude. Navigators have gone north and north-west of it, and found its situation by the declination of the needle. From these poles, lines of magnetic intensity extend to the opposite and corresponding pole of the other hemisphere, and upon or near those lines the needle points north without variation; and toward these lines of no variation the needle every where, on either side declines. The foregoing diagram shows the situation of our magnetic pole and line of no variation, the dip of the needle by the arrows, and the magnetic equator.