Page:Proceedings of the Royal Society of London Vol 1.djvu/251

Rh The observations made by our author upon the north coast are next detailed. The chief differences in the effects of Winds upon this coast, from what they produced upon the south and east coast, are, that a north-east wind raised the mercury as high, if not higher, than one from the south-east; and that a north-west wind, when it came from oil” the sea, and was moderate, was equal, in the above effect, to either of them, and kept the mercury higher than the south-west wind did.

Upon considering the effects of the same winds upon the different coasts of Australia, as described in the foregoing summary of Capt. Flinders’s observations, the following queries seem, he says, to present themselves :

Why do the winds from the north and north-west, which cause the mercury to descend and stand lower than any other upon the south and east coasts, and also in the open sea, and in the south- west bight of the Gulf of Carpentaria, make it rise upon the outer part of the north coast with the same or even worse weather ?

Why should the north-east wind, which occasions a fall in the ba- rometer, 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, causes the mer- cury to rise higher than any other ;—why has it not the same eﬁ'ect upon the north coast and upon the west?

How is it that the south-west wind, which makes the mercury rise and stand high upon the south and west coasts, causes'it to fall be- low the mean standard upon the east coast, and, with the same wea- ther. to descend lower than any other upon the north coast?

The answer to these questions Capt. Flinders considers as suﬂi- ciently obvious; in support of which opinion he offers the following explanation:

The lower air, when brought in by a wind from the sea, meets with resistance in passing over the land ; and to overcome this re- sistance, it is obliged to rise and make itself room by forcing the superincumbent air upwards. The ﬁrst body of air which thus comes in from the sea, being itself obstructed in its velocity, will obstruct the second ; and this 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 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 Will not be able to pass over the top, being kept 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 air will be formed, which at ﬁrst will occupy all the space below a line drawn from the shore to the top of the highest land; but the succeeding bodies of air, at a distance from the shore, will soon feel the effect of the obstruction, and will begin to rise; by which the stratum of lower air will be deeper between the top of the land and the shore, and to some distance from it, than upon the