During the intervals of fine weather the climate is delightful, and the country has a fresh and pleasing appearance; land and seabreezes are as regular as in summer, with the exception, that the latter are much more moderate.
The North-West gales that occasionally occur during the winter months, on the southern parts of the west coast of Australia, are probably felt as far north as Shark's Bay. They blow with great violence, and are accompanied by dark, gloomy weather, and rain. It is then unsafe to be near the land--as the gale that commences at North-North-East, invariably veers to the westward, making a lee shore of the whole line of coast, and between West-North-West and West-South-West blows the hardest.
Fortunately these gales give ample warning; the barometer always foretells their approach, and generally begins to fall three or four days before the commencement of the gale--besides which, there are other never-failing indications of a northerly wind, such as, the change of the current, which (owing to the prevailing southerly winds) usually sets to the northward, but runs strong to the southward during northerly winds--frequently preceding them, and giving more timely notice than the barometer.
A rising of the water is likewise a certain prognostic of a northerly wind; and has been invariably noticed, at Swan River, to precede all gales from that quarter--this, of course, can only be observed while at anchor on the coast.
Another, and perhaps equally certain sign of approaching bad weather, during the winter season (and which is almost certain to be from the northward) is the strength of the North-East winds--as it has been observed, that when the land winds blow strong, particularly from the North-East and the seabreezes are light, with a falling barometer, a gale from the northward will follow. Perhaps these latter remarks, are only applicable to that distance from the shore, where a ship will be within the influence of the land and seabreezes; but as I conceive the limit of that distance to be full 30 miles off shore, a notice of such a symptom of approaching bad weather, may not be altogether useless. I am of opinion, that land winds are at times felt as far off shore as the edge of soundings, which is not less than 30 miles, and generally between that and 40.
(In latitude 30 degrees 25 minutes South and 65 miles from the land, soundings were got from the Beagle, with 185 fathoms of line, upon a coral bottom. Between Swan River and Houtman's Abrolhos, soundings may be had at a greater distance from the land, than off any other part of the west coast.)
The North-West gales are of longer duration, in the latitude of Swan River, and south of that, than they are to the northward; they do not appear to be entirely confined to the winter months, as I am told that a very heavy one was experienced at Swan River, early in March, 1832, and on the 13th December, 1839, the Beagle experienced a strong breeze from the northward, while at anchor in Gage Road, in consequence of which, it was considered necessary to let go an extra anchor.
As it may be satisfactory to know more particularly the progress of these gales, and the effect they have upon the barometer and sympiesometer, I give the details of two that were experienced in H.M.S. Beagle, one at Swan River, in the beginning of June 1838, the other at Houtman's Abrolhos, in the beginning of May 1840; they may be taken as fair criterions of the strength and duration of these gales, the latter having been experienced, probably, within 5 degrees of their northern limit, and the former near the southern extreme of the west coast.
As our barometer had been broken in March 1838, the register of a sympiesometer will be given in describing the gale of June in that year; but as this instrument had been found (by comparison with the barometer) to act exceedingly well, it will be sufficient for our purpose; the GENERAL use of a marine barometer being merely that of a weather glass, for which purpose a sympiesometer is equally good, and more sensitive.
For the gale of 1840, the register of a barometer is shown, which, although 0.2 too low, will serve to show the effect upon the mercury.