Barometric Depressionss

Abstract

I HAVE only just seen Mr. Murphy's criticism on my paper, which appeared in your columns on the 21st ult. I intended that paper as a continuation of one which appeared last year. The former aimed at showing that the ordinary variations of the barometer could not be explained by aqueous vapour; the latter at proving that they were accounted for by the heating and cooling of dry air. Into this question of air versus vapour the earth's rotation did not enter, and I consequently took no account of it in my reasonings. The casual remark, however, which Mr. Murphy fastens on as involving “a serious mistake in the theory of the trade winds,” was almost copied from Article 211 of “Tyndall on Heat;” and as to the matter of fact, I think it is Mr. Murphy, and not Prof. Tyndall or myself, who has fallen into, error. Even if I saw any reason why east and west winds should exactly balance each other on the earth's surface, I could not accept Mr. Murphy's position, that if the earth were of any other shape the trade winds could not proceed from the medial line to the extremities. He assumes that the trade winds are east winds, independently of the shape of the earth, whereas it is just the shape of the earth that makes them east winds. If the earth were a cylinder revolving on its axis, the trade winds (if they could arise under the circumstances) would move directly north and south, and would not be east winds at all; and I can see no reason why they should not extend to the extremity of the cylinder. See “Tyndall,” loc. cit.