1892.] On the Grand Currents of Atmospheric Circulation. 43 



important still, by George Hadley, submitted to the Royal Society in 

 1735.* This George Hadley was a brother of the John Hadley who 

 invented the instrument known as Hadley's quadrant. Hadley's 

 paper is entitled, " Concerning the Cause of the General Trade 

 Winds," and it is right here to notice that he applied the name 

 " general trade wind " not merely to those winds of equatorial regions 

 to which the name trade wind is commonly restricted, but used it as 

 including also the westerly winds known to be prevalent in higher 

 latitudes, and which were taken advantage of in trade by mariners on 

 ocean passages from west to east. Thus, his theory has a much 

 wider scope than the title of his paper would now, according to 

 ordinary nomenclature, appear to indicate. Hadley brought into con- 

 sideration, for the first time, as an essential element towards the 

 formation of a true theory, the inertial and frictional effects resulting 

 in the atmosphere from the rotation of the earth ; and we may with 

 confidence judge that, in that paper, he offered to the world a sub- 

 stantially true theory of a large part of the system of atmospheric 

 circulation in its grandest and most dominant conditions. 



The paper gives a full account of Hadley's theory, accompanied by 

 explanatory remarks, bringing into special notice its most important 

 features ; and the author quotes the concluding passage of Hadley's 

 paper, which he considers, though somewhat vague, and not entirely 

 correct in expression, is to be regarded as suggesting a very notable 

 and important principle, videlicet : — That, in respect to the earth's rota- 

 tion round its axis, the sum of the forward turning-force-influences 

 applied by the winds to the surface of the earth, land and sea in- 

 cluded, must be equal to the sum of all the backward turning-force- 

 influences likewise applied to the earth's surface ; so that these 

 force-influences may be such as conjointly to produce no acceleration 

 or retardation in the revolution of the earth round its axis. 



During a period of more than a century from the promulgation of 

 Hadley's theory there was little, if any, remarkable progress in the 

 development of new speculation regarding the grand or perennial 

 currents of atmospheric circulation. Hadley's theory seems to have 

 lain dormant for a long time in the pages of the ' Philosophical 

 Transactions,' and to have become but little known, even among men 

 of science. Sketches of the theory, more or less complete, were from 

 time to time put forward in encyclopaedias and in works on meteorology 

 and navigation, but usually without due appreciation of its meaning 

 and importance, and often without any reference to his name." On 

 the other hand, progress was gradually being made in the bringing 

 together of information concerning the winds, so far as regards the 

 temporary and local disturbances of the atmosphere ; and speculations 

 or theories were advanced as to hurricanes, tornadoes, or cyclones. 

 * ' Phil. Trans.,' vol. 39, No. 437, for April, May, and June, 1735, p. 58. 



