178 MARINE BAROMETER. 



Observations different coasts of Australia, as deduced from the above exam, 

 and inrerences ,,,,,. 



to ascertain the P'^s, the fol!ovving queries seem to present themselves : 

 correspondent Why do the winds from north and NW, which cause the 

 changes of , , i , i , ■ ,i 



windandwea- "mercury to descend and stand lower than any other upon tlie 



ther, to be ex- foiith and east coasts, and also in the open sea, and in the 

 chan% Lihe ^'^'^^i''- west bight of the guiph of Carpentaria, make it rise upon 

 marine bare- the outer part of the north coast, with the same, or even worse 

 "^^^e"^- weather? 



Wliy should the north-east wind, which occasions a fall in 

 the barometer upon the south coast, considerably below the 

 mean standard, be attended with a rise above the mean upon 

 the east and north coasts ? 



The south-east wind, upon the south and east coasts, caused 

 the mercury to rise higher than any other ; why should it not 

 have the same effect upon the north coast, and upon the west ? 



How is it that the south-west wind should make the quick- 

 silver rise and stand high upon the south and west coasts, — 

 should cause it to fall much below the mean standard upon the 

 east coast, — and upon the north, make it descend lower than 

 any other, with the same weather ? 



The answer, I think, can only be one ; and it seems to be 

 sufficiently obvious. 



The cause of the sensibility of the mercury to winds blowing 

 from the sea and from off the land, may perhaps admit of more 

 than one -explanation ; but the following seems tome to be 

 direct, and tolerable satisfactory. The lower air, when brought 

 in by a wind from the sea, meets with resistance in passing 

 over the land ; and to overcome this resistance, it is obliged to 

 rise, and it will make itself room by forcing the superincumbent 

 air upwards. The first body of air, that thus comes in from 

 the sea, being itself obstructed in its velocity, will obstruct the 

 second, which will therefore rise over the first in like manner 

 to overcome the obstruction ; and as the course of the second 

 body of air will be more direct towards the top of the highest 

 part of the land it has to surmount, than the first was, so the 

 first part of the second body will arrive at the top, before the 

 latter part of the first body has reached it ; and this latter 

 part v/ill be able to pass over the ■ top, being Uept down 

 by the second body and the successive stream of air^ 

 ■whose velocity is superior to it. In this manner, an eddy, or 

 body of compressed, and comparatively inactive air will be 

 formed, which, at first, will occupy all the space below a line 



jdraw* 



