﻿and Fluctuations. 341 



moving from the west. Much of the elastic force due to this 

 compression is lost by some outward movement, whether up- 

 wards, or eastwards through the mountain-passes, or in occa- 

 sional bursts to the westward, when for a time it drives back the 

 advancing current; but the prevailing motion continues, or 

 speedily resumes its course; and the barometer is kept at this 

 very remarkable height throughout the season of strong westerly 

 winds. Mr. Buchan has endeavoured to account for our east- 

 erly winds of spring by a reference to this high pressure*; but 

 he has overlooked the difference of seasons. The easterly winds 

 of this country are the marked feature of April and May ; the 

 high barometer of Siberia is almost peculiar to January. In 

 January we do certainly sometimes get strong easterly winds 

 bringing hard frost; but they are exceptional, and westerly 

 gales (such as the f London' foundered in in 1866) or soft west- 

 erly winds (such as put almost half England under water in 1869) 

 are the more recognized type of January weather. In April 

 and May the barometer in Siberia has fallen to the compara- 

 tively low mean of 29 "96 inches ; but it is then that the air, 

 warmed and expanded by the advancing sun, and no longer 

 forced back by the full strength of the winter west wind, breaks 

 out over the whole of Europe, reaching even to us in the most 

 distant corner of it. I will not at present stop to argue that the 

 strong west wind is really the cause of this high pressure in Ja- 

 nuary; but whether it is or is not, it is equally certain that at 

 that season the winds, not the local, diurnal, and irregular va- 

 riations, but the prevailing winds of Northern Europe and Asia 

 blow towards the place of high pressure f, not from it. 



During the summer months the case is almost entirely re- 

 versed. The west winds of Europe are, as compared with those 

 in winter, both irregular and of very moderate force ; but the 

 barometer in Siberia has at that season a remarkably low mean. 

 The feeble pressure, far from causing a rush of air towards it, 

 permits the previously existing rush to die away ; it is as unable 

 to increase the force of the summer breezes as the high pressure 

 is to control the fury of the winter gales. Relative high tempe- 

 rature is again said to be the cause of this area of low pressure ; 

 but, independently of the reasons already adduced, Siberia is not 

 an area of relative high temperature. Arabia might be called so, 

 or the Punjaub, or the Sahara; but certainly not Siberia, with, 

 in July, a mean temperature of 70° F., a mean which runs nearly 

 on a parallel of latitude across the whole of Europe and Asia ; 

 so that, looking at an isothermal map, and bearing in mind the 



* Handy Book, p. 233. 



t At Barnaul, for instance, Mr. Buchan tables 20 days of west wind in 

 January and 3 of east. — Trans, of Roy. Soc. of Edin. vol. xxv. p. 622. 

 Phil. Mag. S. 4. Vol. 41. No. 274. May 1871. 2 A 



