﻿328 Mr. J. K. Laughton on Barometric Differences 



enough shown by putting an aneroid barometer, with thermo- 

 meter attached, under a glass receiver : the barometer^ which at 

 first will show the pressure of the air in the room, will rise if hot 

 water, fall if iced water is poured freely over the receiver ; the 

 difference of pressure corresponding to a difference of tempera- 

 ture can be exactly calculated by the well-known formula ; but 

 independent of any such careful experiments or calculations, it is 

 within the familiar knowledge of all of us that if a blown bladder 

 be held to the fire it will burst, if it is taken out into the cold it 

 will shrink and become limp and flabby ; the elastic force of the air 

 inside is increased or diminished by the change of temperature. 



From a meteorological point of view, the question then pre- 

 sents itself, whether, in the free atmosphere, expansion takes place 

 in such a way as to cause the increase of volume to exceed the 

 proportionate increase of elasticity, so as, in fact, to lower the 

 elastic force. The view apparently taken by meteorologists is 

 that it does; it is only by such a view that the statement *laid 

 down by Mohn, Buchan, and others can be supported* ; but 

 considering the subject as, in the first place, a branch of prac- 

 tical geography and not of abstract theory, I find no satisfactory 

 basis for such an opinion ; or rather, I should say, I find many 

 instances which stand diametrically opposed to it. 



Foremost amongst these, I may name the Hot Wind of New 

 South Wales and of Victoria. This wind, which bursts out at 

 intervals from the deserts and burning plains of Central Australia, 

 itself dry and burning almost beyond conception, can be attri- 

 buted only to a great and sudden increase of elastic force. It 

 would be foreign to my present subject to speak of the peculiar 

 properties of this wind ; its sudden outburst as a hot wind is all 

 that I have now to do with ; and this sudden outburst seems to 

 me incapable of any other explanation than as the effect of a re- 

 markable barometric rise in the interior of the continent. The 

 mass of air, heated to an extreme degree, and having such aqueous 

 vapour as it contains similarly superheated, has its elastic force 

 enormously increased; it tends to expand with violence, and bursts 

 out towards the place of least resistance ; and it seems to bear 

 stronglyon the question I have proposed, that it finds that place of 

 least resistance always, or almostalways towards thesouth — thatis, 

 towards the place of greatest relative cold. There is not, I believe, 

 any record of a Hot Wind having been experienced on the north 

 coast of Australia; and Stuart, in describing the stony desert 

 which, in his opinion, is the birthplace of the Hot Wind of the 

 south, says very explicitly that, after passing this place, the Hot 

 Wind, which before had been frequent, was never felt till he again 



* Atlas des Tempetes : Christiania, 1870, p. 19. Handy Book of Meteo- 

 rology, second edition p. 47. 



