654 



NATURE 



[July 21, 192 1 



190a. to 240a. {i.e. from 60 to 150 Fahren- 

 heit degrees below freezing point) is cer- 

 tainly cold enough for the purpose, and, for 

 certain reasons which I will not now expound, 

 must be regarded as an effective means of getting 

 rid of heat by radiating it into space. 



The Fly-wheel of the Atmospheric Engine. 

 And what of the fly-wheel and the work done 

 by the engine? Surely" the winds, whether of the 

 general circulation or of the local circulation of 

 cyclonic depressions, are a f^ir representation of 

 the fly-wheel. At the risk of laying myself open 

 to the unpardonable sin of punning, I will point 

 out that the fly-wheel is of enormous importance 

 to flying, because the flyer can either attach him- 

 self to it and be carried along with it, or he may 

 have to labour to make headway against it. The 

 choice of these alternatives depends upon the air- 

 man's knowledge of its habits and behaviour — of 

 its ways, in fact. The constituent parts of the 

 fly-wheel at any time are the natural air-ways of 

 the world. It was by hanging on to one part of 

 the fly-wheel in the fifteenth century that 

 Columbus discovered America, and by the aid of 

 another portion, just two years ago (June 14, 

 igig). Sir John Alcock crossed the Atlantic in 

 16J hours, and on July 13 of the same year Air 

 Commodore Maitland landed R.34 at Pulham after 

 a journey from New York in 3 days and 3 hours. 

 Its total energy is tremendous, of the order of 

 TOO billion horse-power-hours. 



The Polar and Equatorial Circulations in the 

 Upper Air as Parts of the Fly-wheel. 



One of the immediate results of the thermal 

 operations is to maintain the great fly-wheel or 

 to start new sections of it in the form of local 

 cyclonic circulations. Omitting these for the 

 moment, I want to put before you some informa- 

 tion about that part of the fly-wheel w^hich is ex- 

 pressed by the general circulation. We can do 

 so by distinguishing and ultimately isolating those 

 portions of the atmosphere which represent per- 

 manent parts of the general circulation. Our best 

 method of procedure is by way of pressure, \^'e 

 can compute the distribution of pressure for suc- 

 cessive levels and verify the computation by the 

 occasional observations of pressure at the various 

 points of observation. We can thence calculate 

 winds to correspond therewith in accordance with 

 the general principle of the relation of pressure 

 to wind, to which reference has already been 

 ,made, and which finds partial expression in Buys 

 Ballot's law. 



A glass model expresses the results most 

 clearly. It is made to show simultaneously on 

 concentric hemispherical glass shades maps of 

 pressure for 2000, 6000, ^nd 10,000 metres. They 

 disclose an enormous body of air extending at 

 the higher levels from the pole or thereabout to 

 latitude 40°, with a protuberance to the equator 

 in the lower levels of the monsoon region. The 

 air circulates about the polar axis in curves not 



NO. 2699, VOL. 107] 



exactly coincident with circles of latitude, but not 

 very different therefrom. This mass of moving 

 air constitutes a very considerable fly-wheel. 



The maps also disclose a collection of anti- 

 cyclonic circulations in the intertropical region 

 lying between a stream of westward-moving air 

 at the equator and a stream of eastivard-moving 

 air at about latitude 35°. Thus the margins of 

 the anticyclones form a sort of chain-drive pulling 

 the air from east to west on the equatorial side 

 and pushing the polar circulation eastward. These 

 vast local areas of high pressure a^ interesting in 

 relation to the tracks of hurricanes, the normal 

 path of which for this part of the year is marked 

 thereon. The lines which separate the high- 

 pressure areas are at the coast lines, and empha- 

 sise the meteorological importance of those lines ; 

 with one of them the hurricane track is evidently 

 associated. 



Local Cyclonic ( irculations as Parts of the 

 Fly-wheel. 



Among the products of the working of the aerial 

 engine ,we have included the energy of the circula- 

 tion of local cyclonic depressions, whether they 

 take the form of the hurricanes of tropical coun- 

 tries or of the milder depressions of our own lati- 

 tudes. I anticipate no objection to the suggestion 

 that these phenomena are part of the working of 

 the general atmospheric engine ; but there is so far 

 no general agreement as to the precise way in 

 which the engine operates to produce these results. 



I have recently suggested that the development 

 of a vdrtex of revolving fluid may be due to the 

 "injector-effect," or, as I prefer to call it, the 

 "eviction-effect," of rising air or falling rain or 

 both combined, and I have put together an ap- 

 paratus designed to test the effect of the various 

 possible causes in producing a cyclonic vortex 

 when the conditions of relative motion are favour- 

 able. I have come to the conclusion that the air 

 is much more easily moved to take up cyclonic 

 circulation than has hitherto been supposed, and, 

 in fact, cyclonic circulation is the natural expres- 

 sion of a part of the kinetic energy of rising air 

 or falling rain, requiring only favourable local 

 conditions for its obvious manifestation. Perhaps 

 I may add that on that ground a volcano in ex- 

 plosive eruption ought naturally to cause a local 

 tornado. The energy of cyclonic motion can 

 therefore be added to the other parts of the atmo- 

 sphere's fly-wheel with some confidence that it is in 

 accordance with natural fact. 



An Indicator Diagram for the Atmospheric 

 Engine. 



If this view of the atmosphere is a reasonable 

 one, then we ought to be able to refer the opera- 

 tions of the air to what Maxwell calls an indicator 

 diagram^ expressing by the area of a closed figure 

 the work done by the air in the course of a cycle 

 of operations represented by the outline of the 

 figure. During the past forty years I have been 



