October 10, 1!)03.] 



SCIENCE. 



495 



1(1' dynamic meteorology, harmonic analysis 

 has not as yet led to the disclosure of the 

 required generalization. 



I ought to mention here that Professor 

 Karl Pearson, with the assistance of Miss 

 Cave, has been making a most vigorous at- 

 tempt to estimate the numerical value of 

 the relationship, direct or inverse, between 

 the barometric readings at different places 

 on the earth's surface. The attempt is a 

 most interesting one as an entirely new de- 

 parture in the direction of reducing the 

 complexity of atmospheric phenomena. If 

 it were possible to find coordinates which 

 showed a satisfactoi-y correlation, it might 

 be possible to reduce the number of inde- 

 pendent variables and refer the atmos- 

 pheric changes to the variations of definite 

 centers of action in a wa^' that has already 

 been approached by Hildebrandsson from 

 the meteorological side. 



Years ago, when Buys Ballot laid down as 

 a first law of atmospheric motion that the 

 direction of the wind was transverse to the 

 barometric gradient and the force largely 

 dependent upon the gradient, and when the 

 examination of synchronous charts showed 

 that the motion of air could be classified 

 into cyclonic and anticyclonic rotation, it 

 appeared that the meteorological Kepler 

 was at hand, and the first step towards the 

 identification of a working meteorological 

 unit had been taken — the phenomena of 

 weather might be accounted for by the 

 motion and action of the cyclonic depres- 

 sion, the position of the a.scending current, 

 the barometric minimimi. The individual 

 readings over the area of the depression 

 could be represented by a single symbol. 

 By attributing certain weather conditions 

 to certain pai'ts of the cyclonic area and 

 supposing that the depression traveled with 

 more or less unchanged characteristics, the 

 vagaries of weather changes can be ac- 

 counted for. For thirty years or more the 



depression has been closely watched and 

 thousands of successful forecasts have been 

 based upon a knowledge of its habits. But 

 unfortunately the traveling depression can 

 not be said to preserve its identity in any 

 sense to which quantitative reasoning can 

 be applied. As long as we confine ourselves 

 to a comparatively small region of the 

 earth's surface the traveling depression is 

 a real entity, but when we widen our area 

 it is subject to such variations of path, of 

 speed, of intensity and of area that its use 

 as a meteorological unit is seriously im- 

 paired, and when we attempt to trace it to 

 its soui'ce or follow it to its end it eludes 

 us. lis origin, its behavior and its end are 

 almost as capricious as the weather itself. 

 Nor if we examine other cases in which 

 a veritable entity is transmitted can we 

 expect that the simple barometric distribu- 

 tion should be free from inexplicable vari- 

 ations. We are familiar with ordinary 

 motion, or, as I will call it, astronomical 

 motion, wave motion and vortex motion. 

 Astronomical motion is the motion of mat- 

 ter, wave motion the motion of energy, vor- 

 tex motion the motion of matter with energy, 

 but the motion of a depression is merely the 

 transmission of the locus of transformation 

 of energy ; neither the matter nor the energy 

 need accompany the depression in its mo- 

 tion. If other kinds of motion are subject 

 to the laws of conservation of matter and 

 conservation of energy, the motion of the 

 depression must have regard also to the 

 law of di.ssipation of energy. An atmos- 

 pheric disturbance, with the production of 

 rainfall and other thermal phenomena, 

 must comply in some way with the con- 

 dition of maximum entropy, and we can 

 not expect to account for its behavior until 

 we can have proper regard to the varia- 

 tions of entropy. But the conditions are 

 not yet in a form suitable for mathematical 

 calculation, and we have no simple rules 



