NA TURE 



2 iy 



THURSDAY, JANUARY 4, i! 



RECENT CONTRIBUTIONS TO 

 METEOROLOGY. 



Report on the Present State of our Kno-wledge respecting 

 the General Circulation of the Atmosphere. By L. 

 Teisserenc deBort. (London: Stanford, 1893.) 



On Hail. By the Hon. Rollo Russell, F.R.Met.Soc. 

 (London: Stanford, 1893.) 



Weather Lore : a Collection of Proverbs, Sayings, and 

 Rules concerning the Weather. Compiled and arranged 

 by Richard Inwards, F.R.A.S. (London : Elliot 

 Stock, 1893.) 



WHILE meteorologists are generally prepared to 

 admit the salient points of the theory of the 

 atmospheric motions as outlined by Ferrel, there are to 

 be met discussions by various authors, accentuating not 

 only differences in the details of the scheme, but also 

 defects in the theory on which the general circulation of 

 the atmosphere is based. The latest contribution to the 

 literature of the subject illustrating these points, is from 

 M. Teisserenc de Bort, Meteorologist to the Central 

 Bureau, and General Secretary of the Meteorological 

 Society of France; for this authority cannot accept, in its 

 entirety at least, either Ferrel's deductions or his method 

 of conducting the inquiry, Ferrel, it is well known, 

 having deduced the equations for the horizontal motion 

 of the atmosphere, relative to the earth's surface, applied, 

 with effect, the condition of continuity and the law of 

 conservation of areas, or, what would possibly be a better 

 term, the preservation of the moment of rotation, and 

 demonstrated the existence of an easterly motion of the 

 atmosphere in the higher latitudes, and a westerly motion 

 in the lower. To define the limits of these zones, Ferrel 

 remarked that the sum of the moments with reference 

 to the axis of the earth, of the air forming the easterly 

 winds, ought to be equal to that of the westerly winds, 

 and that this condition was fulfilled on a hemisphere, if 

 the easterly winds prevailed up to 30' latitude, and 

 westerly winds to the pole. This line of argument receives 

 some support from the suggestion, that otherwise there 

 would be a residual unexpended force, tending to change 

 the velocity of the earth's rotation. But M. de Bort replies, 

 with some force, that this argument is inadequate, because 

 there is no evidence that the earth's rotation is uniform ; 

 and, indeed, the action of the tides and the diurnal 

 variation of the barometric pressure, point, pretty con- 

 clusively, in an opposite direction. If the effects of friction 

 are omitted, the author seems prepared to admit the 

 validity of Ferrel's argument, and it would be very unjust 

 to deny that Ferrel neglected friction altogether, or failed 

 to modify his original result, obtained without friction. 

 Further, Oberbeck especially has considered the effects of 

 friction, and he has assigned a lower limit to the zone of 

 change of direction not greatly different from Ferrel's 

 value. Apart, however, from this point of theory, the 

 author differs from Ferrel as to the cause of the belts of 

 maximum pressure, north and south of the equator, and 

 adds an explanation of the low pressure zone in latitude 

 55'' and of the polar maximum. 

 NO. T262, VOL, 49] 



But the most interesting, and possibly the most 

 valuable portion of the paper, is the insistance on the 

 connection traced between temperature and distribution 

 of pressure, and the effort to explain the observed vari. 

 ation of pressure along parallels of latitude by the presence 

 of thermic anomalies. The author sees in the variation 

 of temperature over continents and seas in the same 

 latitude, and the consequent changes in the density of the 

 lower strata of the atmosphere, the origin of many of the 

 irregularities that mark the isobaric curves, and a cause 

 not inferior in its effects to the rotation of the earth 

 in establishing the prominent features of the general 

 circulation. 



M. de Bort has also made an ingenious attempt to 

 compute from theory the mean isobars of January and 

 July, and to compare the results with actual observa- 

 tions. This is a step in advance, but the measure of suc- 

 cess that has attended the effort must be left to the de- 

 cision of individual judgment. Two approximations, or 

 two distinct attempts, have been made. In the first, it has 

 been assumed that at an altitude of 16,000 feet the 

 irregularities in the distribution of the isobars disappear, 

 and only the influence of latitude remains. Consequently 

 the observed barometric pressure at the surface should be 

 given by adding to the mean pressure, corresponding to 

 the latitude, the weight of the column of air of variable 

 density e.xtending from the surface to this altitude. When 

 this operation is effected, a comparison with the observed 

 quantity discloses the fact that the computed pressures 

 are too great, and further shows a tendency to exaggerate 

 the barometric minimum over the North Atlantic, while 

 it exhibits a maximum of pressure over North America 

 which does not really exist. There is therefore, admit- 

 tedly, a more marked difference in the computed isobars 

 over continents and seas than is actually observed. Two 

 causes are assigned for the failure to reproduce actual 

 facts, both of which are probably operative. The one is 

 that the density of the column of air does not diminish 

 uniformly with the temperature, which hypothesis, for the 

 purpose of computation, it is necessary to assume. The 

 other is that probably the slope of the surfaces of equal 

 pressure from the equator towards the poles is greater 

 where the temperature is already low, than where the 

 temperatures are high, in the upper regions of the 

 atmosphere. 



The second attempt to reproduce the observed pressure 

 is arranged to take into account the influence of the un- 

 equal distribution of temperature upon the form of the 

 upper isobars, and it is contended that the computed 

 values of the surface pressure " show close analogy with 

 those representing the isobars deduced from direct 

 observation.'' 



Not content with surveying the conditions of our 

 atmospheric circulation, the author proceeds to discuss 

 those that obtain on the planets, and submits two ideal 

 pictures of the earth with its surrounding cloud as seen 

 from space. These are compared with a photograph of 

 Jupiter, but we strongly doubt whether the author gleans 

 any additional facts in support of his views. The red 

 spot is a conspicuous feature in this photograph, and 

 whatever may be the true explanation of that phenomenon, 

 the tolerable permanence of its character forbids us to 

 ascribe it to atmospheric circumstances. But M. de Bort 



