582 MR ALEX BUCK AN ON THE MEAN PRESSURE OF THE ATMOSPHERE 



takes a direction intermediate, approaching, however, more nearly to the direc- 

 tion and course of the circular curves than of the radii to the centre." Or, 

 according to Dr Buys Ballot, the angle is not a right angle, but from about 

 60° to 80°. This relation is usually called "Buys Ballot's Law of the Winds." 



Another well-marked depression is the low summer pressure in the interior 

 of Asia ; with reference to which, it is seen from the charts that the winds of 

 Eastern Europe and Western Asia are from N.W. to W.N.W. and W. ; at Ceylon, 

 S.W. ; at Shanghai, S.E. ; and on the Sea of Okotsk, N.E. ; whilst in the interior, 

 calms generally prevail. 



The behaviour of the winds, as regards the low pressure of North America, 

 is exactly similar to that of the winds in Asia at this season. In all these cases 

 the wind appears to flow round and in upon the space where pressures are 

 low. Even in those instances where the depression over a limited space is com- 

 paratively small, such as in Australia during the summer months, the winds 

 observe the same course with respect to it. 



A well-known and remarkable diminution of pressure is that of the Antarctic 

 regions ; and though, except in Tasmania and the south of New Zealand, obser- 

 vations are wanting at particular points for a sufficiently long time to give good 

 averages, yet the concurrent testimony of sailors and the inhabitants of these 

 regions all go to show that, at least on the outskirts of the region, winds are 

 chiefly N.W. or W.N.W. — that is, they appear to flow in upon the space of low 

 pressure. The low pressure in the equatorial regions, towards which the trades 

 blow, is an illustration of the same principle. 



Winds within, or near, a sjmce of High Pressure. — The most prominent illus- 

 tration of this is the high pressure in the interior of Asia in winter. It is seen 

 from a single glance at the charts that the winds flow out of this space in every 

 direction. The same outflow is seen with respect to the less strongly marked, 

 but still very distinct space of high pressure in North America ; owing to the 

 large number of stations available here, this principle is amply illustrated. 



The next most noteworthy area of high pressure occurs in summer between 

 Africa and North America, out of which also the charts show the winds blowing 

 in all directions towards and round upon the surrounding low pressures. 



The following mean pressures, in inches, at 32° and sea-level, occur in Australia 

 in June : — At Brisbane, Queensland, 30 062 ; Sydney, 30-116 ; Melbourne, 30T78; 

 Adelaide, 30T32; Freemantle, 30121; and at Deniliquin, in the interior, on a 

 branch of the Murray River, 3J*217. Hence a higher pressure occurs at this season 

 (winter) in the interior, and it may be inferred that it is greatest in the southern 

 portion of the interior. The prevailing winds are these : — At Brisbane, S.S.W. ; 

 Sydney, W. by N.W. ; Melbourne, N. ; Adelaide, N.E. by N. ; Freemantle, N.E. 

 by E. ; in other words, the winds blow out from this space of high pressure. 



This behaviour of the winds with respect to spaces of high pressure differs in 



