Meteorology in its connection with agriculture / by Joseph Henry.

  • Henry, Joseph, 1797-1878.
Date:
1858
Catalogue details

Licence: Public Domain Mark

Credit: Meteorology in its connection with agriculture / by Joseph Henry. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    the north: these hooks ■would represent the planes in which the currents of the air would circulate in the northern hemisphere, were the earth at rest; hut if the earth is supposed to he in motion, then the hooks must he inclined to the west, so as to make an acute angle with the horizon, and overlap each other like the inclined strata in a geological model. If on each leaf of each hook a circuit of arrows he drawn, then will the assemblage of these represent the paths of the diiferent atoms of the atmosphere. The currents of air, however, would not be in perfect planes, but in surfaces which could he represented by bending the leaves to suit the curvature of the earth. In this manner would be exhibited the general motion of the wind, which has been determined by actual observation. The greater portion of the circulation would descend to the earth within 30 degrees of the equator, giving rise to the trade winds ; a portion would flow further north, and produce the southwest winds; another portion would extend still further northward, descend to- wards the earth as a northwest wind, and so on. The air which descends in the region of the pole would not flow directly southward, but, on account of the rotation of the earth, would turn-towards the west and become a northeasterly current. At first sight it might appear that the north wind which descends from the polar regions would continue its course along the surface until it joined the trade winds within the tropics ; but this could not be the case, on account of the much greater western velocity this wind would acquire from the rapidly increasing rotary motion as we leave the pole. There would, therefore, be three distinct belts in each hemisphere, namely: the belt of easterly winds within the tropics, the belt of westerly in the temperate zone, and the belt of northwesterly at the north. The existence of these belts has been clearly made out by Professor CoflSn in calculating the resultant of all the winds of the northern hemisphere, or, in other words, by eliminating the effects of extra- neous action, and exhibiting the r-esidual as the result produced by the general circulation. Another condition, however, must be introduced. These belts would not be stationary, hut would move laterally towards the south or the north, according to the varying positions of the sun at different seasons of the year. Their breadth would also vary; be- cause they would be crowded into a smaller space towards the pole in the winter, and expanded into a wider space in the summer. To trace with precision, while under these varying perturbing influences, the path which would be described by a particle of air in its circuit, transcends the power of unaided logic, and can only he accomplished, if at all, by means of the most refined mathemati- cal artifices. This problem has lately, it is believed, been presented as one of the prize questions of the French Academy of Sciences. Were it, however, solved, with all the conditions that have been assigned, this would not be sufScient; since there is another cause of disturbance, perhaps more active than any yet enumerated, namely; the condensation of the vapor which arises from the sur- face of the ocean and is carried to different parts of the earth by the