Matthew Fontaine Maury, Lieutenant, U.S.N.

“ The extra-tropical part of New Holland comprises a portion of land thus situated in the southern hemisphere. Tropical India is to the northward and westward of it; and tropical India is in the northeast trade-wind region, and should give extra-tropical New Holland a slender supply of rain. But what modifications the monsoons of the Indian Ocean may make to this rule, or what effect they may have upon the rains in New Holland, my investigations in that part of the ocean have not been carried far enough for final decision ”

“ I know of no law of nature or rule of philosophy which would forbid the supposition that the air which has been brought along as the northeast trade-winds to the equatorial calms does, after ascending there, return by the counter and upper currents to the calm zone of Cancer, here descend and reappear on the surface as the northeast trade-winds again. ”

“ Reason suggests, and philosophy teaches, that, going from a lower to a higher temperature, the evaporating powers of these winds are increased; that they have to travel, in their oblique course toward the equator, a distance of nearly three thousand miles; that, as a general rule, they evaporate all the time, and all the way, and precipitate little or none on their route; investigations have proved that they are not saturated with moisture until they have arrived fully up to the regions of equatorial calms, a zone of constant precipitation. ”

“ Infusoria are sometimes found in sea-dust, rain-drops, hailstones, or snow-flakes; and if by any chance it should so turn out that the locus of any of the microscopic infusoria which might be found descending with the precipitation of the Arctic regions should be identified as belonging to the regions of the southeast trade winds, we should thus add somewhat to the strength of the many clews by which we have been seeking to enter into the chambers of the wind, and to “tell whence it cometh and whither it goeth.” It is not for man to follow the “wind in his circuits;” ”

“ The polar calms are no more a point than the equatorial calms are a line; and, considering that these poles are areas, not points, is it not a little curious that philosophers in different parts of the world, using different data, and following up investigation each through a separate and independent system of research, and each aiming at the solution of different problems, should nevertheless agree in assigning very nearly the same position to them all? ”

“ Now observations have shown that the winds represented by H are rain winds; those represented by B, dry winds; and it is evident that A could not bring any vapors to these calms to serve for H to make rains of; for the winds represented by A have already performed the circuit of surface winds as far as the pole, during which journey they parted with all their moisture, and, returning through the upper regions of the air to the calm belt of Cancer, they arrived there as dry winds. The winds represented by B are dry winds ”

“ But the brown fields in summer afford evidence on a larger scale, and in a still more striking manner, of the fact that, in nature, columns, or streamlets, or curdles of air do readily move among each other without obstruction. ”

“ If it did not, the proportion of land and water, and consequently of plants and warm-blooded animals, being so different in the two hemispheres, we might imagine that the constituents of the atmosphere in them would, in the course of ages, probably become different, and that consequently, in such a case, man could not safely pass from one hemisphere to the other. ”

“ Therefore it is fair to suppose that much of the vapor which is taken up on that side of the equator is precipitated on this. The evaporating surface in the southern hemisphere is greater, much greater, than it is in the northern; still, all the great rivers are in the northern hemisphere, the Amazon being regarded as common to both; and this fact, as far as it goes, tends to corroborate the suggestion as to the crossing of the trade-winds at the equatorial calms. ”

“ Accordingly, if this process of reasoning be good, that portion of South America between the calms of Capricorn and Cape Horn, upon the mountain ranges of which this part of the atmosphere, whose circuit I am considering as a type, first impinges, ought to be a region of copious precipitation. Now let us turn to the works on Physical Geography, and see what we can find upon this subject. ”

“ That tremulous motion which we so often observe above stubble-fields, barren wastes, or above any heated surface, is caused by the ascent and descent, at one and the same time, of columns of air at different temperatures, the cool coming down, the warm going up. ”

“ If it depended upon chance whether the dry air should come out on this side or on that of this calm belt, or whether the moist air should return or not whence it came — if such were the case in nature, we perceive that, so far from any regularity as to seasons, we should have, or might have, years of droughts the most excessive, and then again seasons of rains the most destructive ”

“ Here the outcroppings of the relation between magnetism and the circulation of the atmosphere again appear. May we not find in such evidence as this, threads, attenuated and almost air drawn though they be when taken singly and alone, yet nevertheless proving, when brought together, to have a consistency sufficient, with the lights of reason, to guide us as we seek to trace the wind in his circuits? The winds (§ 106) approach ”

“ One such source of light comes from the observations of my excellent friend Quetelet, at Brussels, which show that the great electrical reservoir of the atmosphere is in the upper regions of the air. It is filled with positive electricity, which increases as the temperature diminishes. ”

“ It then escapes by an opening upward, the cross section of which is sixty or one hundred, or even three hundred miles. A very slow motion upward there will carry off the air in that direction as fast as the two systems of trade-winds, with their motion of twenty miles an hour, can pour it in; and that curds or columns of air can readily cross each other and pass in different directions without interfering the one with the other, H or at least to that degree which obstructs or prevents, we all know.
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