﻿340 Mr. J. K. Laughton on Barometric Differences 



high in the months of July and August ; and it is quite certain 

 that the wind at that season blows strong up the river* — blows 

 towards the place of high pressure, not from it. One direct and 

 unmistakable contradiction is sufficient to overthrow any axiom; 

 and an instance such as this deals a most severe blow on the 

 particular axiom which has been proposed for the guidance of 

 meteorologists. If wind does not always blow from the place of 

 high pressure, but in some instances blows straight on end to it, 

 it is quite clear that the one part of the proposed axiom is false, 

 and that we are at liberty to reject the other — to say, in short, 

 that winds are not always caused by differences of barometric 

 pressure. Winds cannot blow from the place of low to the 

 place of high pressure if differences of pressure are the cause of 

 the winds ; when, therefore, we find winds distinctly and for a 

 length of time blowing towards the place of high pressure, we 

 feel sure that they are not doing so by reason of any mere dis- 

 turbance of hydrostatic equilibrium ; we are confident that the 

 difference of pressure is not the cause of such winds, although, 

 indeed, such winds may well be the causes of the difference of 

 pressure. 



The valley of the Amazon, however, is only one locality in 

 which the meteorological axiom I have referred to is palpably 

 controverted. Nor is it the most decided. A still clearer in- 

 stance of the failure of the law is offered by the high barometer 

 of Eastern Siberia in the winter months. One of the so-called 

 poles of cold is in this district ; and it has been conjectured, and 

 indeed very positively stated, that the extreme cold, by increas- 

 ing the density of the air, is the direct cause of the high pres- 

 sure — an opinion which I have shown to be neither theoretically 

 correct nor conformable to geographical evidence; for the baro- 

 meter near the other northern pole of cold, in North America, 

 stands low, as it does also in the antarctic regions. Leaving, 

 then, the low temperature out of consideration, as a condition 

 which cannot possibly produce such very opposite effects, and 

 examining into the points of difference between these places 

 which resemble each other in their extreme cold, we find that to 

 leeward of Siberia is a lofty and difficult extent of mountainous 

 country. The prevailing wind of winter is west or north-west ; 

 and almost impenetrable mountain-ranges bar its progress to- 

 wards the east or south. Into the angle between these ranges 

 air is continually driven, and acquires an elastic force tending 

 towards equilibrium, not against the statical pressure of the air 

 to the westward, but against the dynamical pressure of the air 



* Bates, "Naturalist on the Amazons/ vol. ii. pp. 13, 21. Maury, ' Ba- 

 rometric Anomalies about the Andes * in Silliman's American Journal of 

 Science, 2nd ser. vol. xix. p. 385. 



