28 Dr. W. N. Shaw. On the General [May 16, 



are easily calculable, may have very important consequences in relation 

 to classifying the facts within our knowledge of weather changes in 

 middle latitudes. It seems to follow directly that easterly winds are, 

 as a rule, winds of relatively speaking low altitudes, due to surface 

 temperature, arid that local areas of high pressure, with an anti-cyclonic 

 circulation, may lie underneath regions of general westerly flow in the 

 upper air. 



Another conclusion that follows directly from this method of 

 analysis of the distribution of forces corresponding to the surface 

 circulation, is the confirmation that it affords of the suggestion of the 

 existence of a high-pressure area over the Antarctic Continent, made 

 by Sir J. Murray, in the discussion of the " Challenger " observations. 

 Such indications of the results of Antarctic explorations as have been 

 already received are consistent with the suggestion,* and the detailed 

 results of the recent expeditions must furnish very valuable additions 

 to the material for the study of this interesting question. It is clear 

 that the effect of the component, due to the lower atmosphere in the 

 southern latitudes, will become intensified where the intensity of the 

 low temperatures becomes effective; and the pole of extreme cold, 

 which in the southern hemisphere must be nearly coincident with the 

 geographical pole, will have associated with it a component distribu- 

 tion for easterly circulation similar to the low-temperature pole of 

 north-east Siberia, in the northern hemisphere. The intensity of the 

 cold in the south polar regions is undoubted, and the existence of the 

 distribution for an easterly circulation round a high-pressure centre, 

 due to the weight of the lower air, follows directly therefrom. 



A third effect of the distribution of pressure in lower regions of the 

 atmosphere, and the corresponding air circulation, may perhaps be 

 traced in the series of wind charts of the South Atlantic already 

 referred to, where there is obvious evidence of a tendency of the winds 

 to run tangentially to the coast line. The coast line is equally 

 obviously a line of separation between regions of different surface 

 temperature distribution, and hence a locality of steep temperature 

 gradient. Thence follows a steep pressure gradient for the lower 

 atmosphere, and associated therewith a distribution favourable for the 

 flow of air in opposite senses on the two coast lines for the same 

 latitude. 



The division of the atmosphere into an upper and a lower stratum 

 at the 4000 metre level is perfectly arbitrary, and that level is only 

 chosen because M. Teisserenc de Bort selected it for constructing his 

 charts of mean isobars of .the upper air 18 years ago.f It is in the 



See Mr. Bernacchi's paper on "Winds and Temperature at Cape A dare " in 

 ' Magnetic and Meteorological Observations made by the " Southern Cross " 



Antarctic Expedition ' (published by the Royal Society), pp. 40 and 49. 

 t ' Annales du Bureau Central Meteorologique de France,' 1887, Part 1, 



p. Cl. 



