212 



NATURE 



[May 4, 1916 



crucial test of the two theories. If an anticyclone is 

 a place where air descends and flows outward, its 

 velocity should diminish as the air spreads outwards; 

 but the reverse is the case with an antrcyclone. 



2. The small influence of the troposphere, and there- 

 fore the dominance of the stratosphere, in the dis- 

 iribution of surface pressure. 



This follows directly when numerical values are 

 inserted in equation A. The right-hand side of the 

 equation consists of two terms which are of opposite 

 sign and, numerically, approximately equal in the 

 middle regions of the troposphere. Their combined 

 effect for the whole range is therefore relatively small, 

 and the change of pressure produced in the tropo- 

 sphere is unimportant. The distribution of the strato- 

 sphere is dominant throughout the troposphere. 



3. The apparently capricious variations of wind and 

 temperature -with height disclosed in pilot-bailoon 

 ascents and by ballons-sondes. 



The results of the observations of ballons-sondes 

 show local variations of temperature and those of the 

 observations of pilot balloons show similar variations 

 of the direction and velocity of wind. These varia- 

 tions can be connected numerically by Equation A in 



RELATION or WIND ELEMENT? TO HEIGHT. 



VELOCITY 

 10 to 



DIRECTION 



son 



Fig. I. — Diagrams showing the falling off of wind velocity in the 

 stratosphere (about ii kilometres). The scale on the left gives the 

 heights in kilometres, those at head and foot the velocity tn metres 

 per second, and the direction in degrees from north respectively. 



combination with Equation i. A number of examples 

 are given in a paper read before the Royal Meteoro- 

 logical Society. To quote one, the rapid transition 

 from a southerly wind at iioo metres through a calm 

 to a northerly wind at 1500 metres on October 16, 

 19 13, was shown to indicate a temperature gradient of 

 7° per hundred kilometres towards the east, a condition 

 that was in satisfactory accord with the meteorological 

 circumstances of the time. 



The same combination of equations enables us to 

 specify the conditions under which " Egnell's law," 

 that wind velocity at different heights is inversely 

 proportional to the density at those heights, may be 

 expected to be verified and the conditions prescribed 

 are essentially reasonable. 



4. The rapid falling off of wind in the stratosphere 

 noted in observations with pilot balloons. 



This is illustrated by Fig. i, a diagram compiled 

 from the figures of high soundings reproduced in 

 Captain Cave's "Structure of the Atmosphere in Clear 

 Weather." The result follows directly from the ap- 

 plication of Equation B to the special conditions of 

 the stratosphere. The computation.s for the four 

 occasions in which there was a wind of considerable 



NO. 2427, VOL. 97J 



magnitude at the base of the stratosphere give the 

 following results : — 



Date 



1908 



October 

 July 31 

 July 29 

 July 28 

 July 27 



Rate of change 



of velocity in 



the stratosphere 



m/s per 

 kilometre 



- 7 

 ~ 5 



— II 



-13 



HorizontAl temperature gradient 



Computed. 



Degrees 



per 100 



kilometres 



2-1 



1-5 

 3-3 

 40 



Observed. 



Drgrces 



per 100 



kilometre'! 



3-3 



25 



The calculation has been arranged to give the com- 

 puted horizontal temperature-gradient, because the 



Fig. 2. — Glass model showing the disiribution of temperature in the 

 atmo.sphere on July 27, 1908. Isotherms are drawn for every 

 5° A., and the thickness of each line represents half a degree 

 except in the ca.<ie of the isotherm of 273°, which is covered by 

 a band 5° in width. The height of the model represents 24 

 kilometres. The tilting upward of the isothermal lines shows the 

 commencement of the stratosphere at about 11 kilometres. 



values of that quantity can be taken directly from the 

 models of temperature distribution constructed in the 

 Meteorological Office for July 27 and 29, Figs. 2 and 3. 

 The order of magnitude which is indicated is quite 

 reasonable, and for the one occasion on which the two 

 can be compared the agreement turns out to be exact. 

 That may be fortuitous ; but we may take advantage 



Fig. 3.^Model showing the distribution of temperature in the 

 atmosphere on July 29, 1916. In each case the model stands on 

 a map of the British Isles upon which the isobars are shown.* 

 In the interval of two days a layer of cold air spread it.self 

 along the base of the stratosphere from the east, and raised the 

 surface pressure by about 10 ml. 



of the circumstance to use the combination of the figures 

 for the wind In the stratosphere and the horizontal 

 temperature gradient at 13 kilometres to compute 

 the latitude of the place of observation with an 

 accuracy that may lead us to reconsider the common 

 remark that meteorology is not an exact science. 



The same equation applied to the troposphere, 

 assuming normal values for temperature, gives cor- 



