200 Prof. J. D. Everett on the General Circulation 



prevalent south-west winds in north temperate latitudes in a 

 more satisfactory manner than by Maury's supposed crossing of 

 the upper and lower currents near the Tropic of Cancer. 



Three years later, Mr. W. Ferrcl, A.M., Assistant upon the 

 American Ephemeris and Nautical Almanack, published (in 

 vols. i. andii. of the f Mathematical Monthly') a series of articles 

 " On the Motions of Fluids and Solids relative to the Earth's 

 Surface, comprising Applications to the Winds and the Currents 

 of the Ocean." Mr. Ferrel begins by referring to a pamphlet 

 which he published on the same subject a few years previ- 

 ously, and concludes by pointing out an important modifica- 

 tion in one part of his theory as first published, a modifica- 

 tion which he has seen it necessary to make after reading the 

 Report of Professor Thomson's paper in the British Association's 

 Proceedings. Mr. Ferrel's paper, as reprinted from the ' Mathe- 

 matical Monthly,' occupies seventy-two pages, of which about 

 sixty are occupied with an elaborate mathematical investigation 

 of the distribution and motion of the atmosphere which would 

 result from the rotation of the earth combined with the heating 

 of the equatorial regions on the hypothesis of no friction. In 

 the latter part of the paper the modifying effects of friction are 

 mentioned, and a theory of general atmospheric circulation, as 

 actually existing, is laid down in such language as to be intelli- 

 gible to those who are not able or willing to follow the steps of 

 the mathematical investigation. 



Without discussing the question of priority, I may say that 

 the views advanced by Mr. Ferrcl and by Professor Thomson 

 arc substantially the same, as far as they are comparable; but 

 Mr. Ferrel's views are much more fully developed and applied. 



As the theory propounded by these two authors (which may 

 appropriately be called the centrifugal theory of atmospheric dis- 

 tribution and circulation) is, I believe, very little known among 

 meteorologists, I think I shall be doing good service in calling- 

 attention to it, and in pointing out how some of the numerical 

 quantities involved may be calculated without the aid of the 

 higher analysis employed by Mr. Ferrcl. 



Since the first draft of the present paper was written, a letter 

 has appeared from Mr. Ferrcl in ' Nature' (July 20), in which 

 he calls attention to some of his principal results, and presents 

 some points rather more clearly than in his earlier publications. 



that of George Hadley, who published it in the Phil. Trans, for 1735 (vol. 

 xxxix. p. 58). Hadley appears to have been the first to point out the true 

 connexion between the earth's rotation and the easting of the trade-winds. 

 Halley, in 168G (Phil. Trans. No. 183), had indicated the existence of a 

 circulation of air between the polar and equatorial regions, due to differ- 

 ence of temperature, but he erroneously attributed the casting of the trades 

 to the diurnal wave of heat which runs round the earth from east to west. 



