Meteorological Notes

Abstract

ATMOSPHERIC MOVEMENTS.—A first paper on this subject, by Mr. Ferrel, has been published by the United States Coast Survey Office, in which the inquiry is limited to an investigation into the mechanics and general motions of the atmosphere which are dependent on wide-spread and periodically-recurring disturbances. In consideration of the enormous difficulties in the way of investigating the effects of friction, the author adopts the only course open to him, viz., to introduce unknown functions into the equations representing the resistances from friction in the direction of the co-ordinates, leaving these to be determined approximately from a comparison of the final results deduced from the equations with observation. From a mathematical examination of the question it is concluded that in whatever direction a body moves upon the surface of the earth, there is a force arising from the earth's rotation tending to deflect it to the right in the northern but to the left in the southern hemisphere; and that this deflecting force is exactly the same for motions in all directions, so that if any sensible effects of this sort arise in the case of rivers or of railroads running north or south, the very same effects must take place where they run east or west or in any other direction. The amount of this deflecting force is exactly double of that which is obtained in accordance with the principle adopted by Hadley. An elaborate examination is made of the distribution of temperature over the earth, the most important of the results being that the mean temperature of the whole surface of the earth is 60°.2, the mean for the northern hemisphere being 59°.5, and that for the southern hemisphere 60°.9. With reference to this result Mr. Ferrel remarks that if important data collected by Dr. Hann for the extreme southern latitudes had been at hand while he was engaged with the investigation, the results obtained for the mean temperatures of the two hemispheres might have been nearly equal. This result, which is essentially different from the commonly received opinion, has, it is obvious, important bearings on many questions of terrestrial physics. The distribution over the globe of atmospheric pressure is similarly examined with results of great importance in their relations to meteorological theories. The coefficient of the annual inequality of pressure in North America amounts to only about one-third of that of the interior of Asia, from which the important conclusion is drawn that the difference between Asia and America in this respect does not depend so much upon the difference in the extremes of temperature of the two continents, which is inconsiderable, as upon the difference in the extent of the two continents. The annual maximum of barometric pressure for the United States, except the Pacific coast, occurs about December 23, which is about sixteen days earlier than in Europe. In both continents the time is considerably earlier than the time of the minimum of temperature. The distribution of temperature and pressure and the prevailing normal winds of the globe are shown on seven well-executed maps. In succeeding papers Mr. Ferrel intends to investigate those disturbances in the distribution of temperature and humidity which are of a comparatively local character, and which result in the locally developed phenomena of cyclones and other storms; and finally to apply the principles of atmospheric mechanics thus developed to the explication of oceanic currents.