Since the invention of the barometer, it has excited the attention of so many scientific men, and so many of their remarks upon it are already extant, that I fear it would be wasting time to say anything more regarding its properties or utility. If however, the little I have to say be found useful even to one person in command of a vessel, the purpose for which this is written will be accomplished.
If there is anything in nature that will assist us in studying the barometer, it is the approach of daylight, yet it does not appear to have come under the notice of many. The various philosophical works I have read are equally silent upon the subject. In a long treatise or chapter on twilight in an astronomical work by no less a person than Herschel, I sought with a fruitless result for some information on the subject. The only writer I have found whose attention it appears to have arrested is Captain Fitzroy, who tells us in the " Beagle's Voyages," p. 285, vol. ii., " When the first streak of light appeared close to the horizon, and the sun's. rising was preceded by a glow of faint red, not extending far, a fine day succeeded, whether the sky were then overcast or clear ; but if the first gleam of light appeared high above the horizon, behind clouds, and there was much red, not only near the sun, but visible on clouds near the zenith, wind, if not rain, was sure to follow," This is the sum of all that I have read upon the matter, and it may perhaps not be improper to extend it. Whenever the coming in of the morn can be observed, if light first appears below the altitude of 5° or 6° very fine weather may be depended on, at least until sunset. If any clouds are in the direction of sunrise, they will be in small fragments of cumulus, in figures of islands, castles, churches, &c., slowly changing their shape, and nearly stationary. Sometimes, however, the largest cumulus prevails, resembling large broken stacks of wool.
If there be an overcast aloft, it will be of thin light stuff, that generally retires or disappears soon after sunrise, with a clear expanse, stars in and near the zenith will remain visible long after you lose sight of those below the altitude of 15° or 20°, and in this appearance consult the barometer, it will be high let the wind yon have be blowing in whatever direction it may, land, ships, and all objects will be seen at an immense distance. If you should be within the tropics, you may observe the zenith cirro-cumulus slowly changing its formation to that branch of cirro-stratus, the mackerel sky ; and again, rechanging, it may be hours in this manner ; its motion, if any, will be in a contrary direction to the wind generally.
When day dawns at about the altitude of 20, or upwards, large black clouds, shaded red as the sun rises, or if smokey and bronzed, wind and rain will follow before next-rise and you have a sinking barometer. If you are in the southern hemisphere, northerly or N.E. will be the direction, but mostly in the eastern board; and, in this instance the glass may be rising. If near land, it will be effected in the following form (after many years' observation) : in the northern part of the North Island of New Zealand, N., or N .N. E , from the North Cape to the Bay of Plenty ; Bay of Plenty to Cook's Strait, E. N. E. to E S E. through the strait S.E. ; Cook's Strait by Foveaux Strait, east generally, or at Banks Peninsula S.E., through Foveaux Strait S.E., which may be expected every new and fall moon in summer in the southern ocean, though not at all times of long duration.
When day dawns above 20°, strong breezes may be looked for, or will be blowing. If mackerel sky prevail over head, with long horizontal lines of cirro-stratus above the altitude of daybreak, their edges being hard and well defined, an increasing breeze will terminate. the day ; but if the horizontal lines are below the altitude of dawn, their edges will be less hard and defined, and any increase of wind seldom follows.
Always rest assured that the higher dry dawns the heavier the gale ; and with sufficient clearance of clouds, stars in the zenith will be lost sight of before those at a low altitude. However strange this may appear, careful and constant observation will soon render it simple and clear.
If, however, no dawn can be observed, as in cloudy weather, the horizon being everywhere closed in with dense masses of dark dirty-looking grey and black cumulo-stratus, or more properly speaking, compact bodies of nimbus, the gale is approaching, your barometer is on the decline, or is down ; and its rate of depression is about 1/10th per hour ; a good barometer giving you at least sixteen hours' notice. I have known some men quite offended with the barometer because the gale did not follow its immediate descent.
In looking over the account of the hurricane at Antigua, in August; 1835, as given by Lieut. B. Gravelink, of the Dutch Royal Navy, p. 131, Ethiopic Directory, he informs us that, " On the morning of that day, in which this hurricane happened, the sun rose as beautifully as ever, a clear expanse and a gentle breeze gave reason for expecting fine weather."
Here I must beg leave to offer some remarks, and if they differ from the above account, which they will do, they are written with good feeling and respect due to a man of talent and a valuable member of society, and I trust I shall be warranted in so doing, by giving such notices of the weather in all climes, that will enable an observer to be prepared at least a few hours beforehand for the destructive operation.
There could have been no better appearance than having a clear expanse for taking a careful observation of those notifiers of the weather which nature at all times sets up before as.
Indications of hurricane, or storm, may be observed by the first show of light appearing directly overhead, and with the clear expanse above-mentioned, it is probable that stars of less magnitude will not be visible to the naked eye during the whole night, if the elemental eruption is to take place in daytime as above stated, at all events they will disappear soon after midnight, stars of the first class that are visible will be ill-defined in their edges, because it is evident they will be seen through a thick dry atmosphere, although it may be cloudless. If it be perfectly clear to the eastward, as in the aforementioned account, the sun may rise clear (that is of clouds,) and bright, but not beautiful ; it will rise with an angry aspect, and of pale brassy, or fiery brightness, with an aspect denoting, is accordance with the first coming of light, all that subsequently followed on that day, and these forewarnings of nature are as sure and simple on these occasions as her operations are dreadful and destructive.
It is, however, greatly to be regretted, that in the account given by so able a person as Lieutenant Gravelink, that no mention whatever is made of the barometer, as it generally indicates those violent changes in a descent of 1-10th of an inch per hour, for at least five or six hours, previous, and had notice been taken of the indications of a good barometer, some guidance for the coming of another hurricane might have been obtained. Barometers will generally be found to have descended their full depression at least three or four hours before the storm sets in, and will often rise when the gale is at its height, because when the gale is at its greatest weight of force at the earth's surface, the air at an altitude of one or two miles from the earth's surface is restoring its equilibrium. The observations on the barometer made by the Hon. J. C. Lees, chief justice of Nassau, are worthy the attention of all traders in that part of the world, and the following remarks when he tells us that the barometer - stands highest when the wind is N.E., and fails lowest when it is N.W." Upon careful observation this will be found to be precisely the working of the instrument in the whole South Pacific, south-ward of 30°, including New Zealand, Van Diemen's Land. and New South Wales. The honorable gentleman farther adds, " when during the hurricane months, the barometer falls much and rapidly, preparations ought to be made for rough weather;" but in continuation he does not inform us what constitutes. "much and rapidly," because time, the only thing by which we can properly mark its progress, is not taken into account ; pay due notice to its rate of depression, and something like a correct, data maybe obtained to secure us from some of the destruction at a subsequent period.
I have remarked upon the east coast of New Zealand, the indications with the N.E. gale will be 30.70, or something thereabouts ; but on the western coast a gale of the same force and direction, the indication will be 29.90, or nearly so. The only observer of such variation of indications, that I have met with to accord with me in this remark, was Mr. Parker, master of H.M.S, Hazard. The question will now arise whether it would be reasonable to infer that the barometer is under the influence of local attraction?
It will, however, be found to descend with rain in both the North and South Pacific unless near the equator.
In the sea of Kamschatka, and its neighbourhood, the fogs wonderfully depress the mercury, although there maybe a continuation of light winds.
In Bennett's " Voyage round the World," the same thing is mentioned, and I think Captain Beechey, in his " Voyage in the Blossom," makes the same remark ; but it will chiefly be found in those depressions occasioned by dense atmosphere, that the fall is very gradually.
In p. 375, sec. 8, of the Ethiopia Directory, some account is given of a heavy N.W. gale at the Cape of Good Hope, " It continued." says the account " several days, drove several ships on shore. &e., barometer being in 29.5, which is rather high for a gale of that nature. its direction being N.W. and if its depression during the stale was not below the statement of 29.6, some local cause may probably be assigned. However, the account as it stands, is wholly destitute of any information for the guidance of mariners. Shortly after rounding Cape Horn, from the westward. I was greatly surprised to see 30.38 indicated with a gale at the north, is lat. 44° S., long. 49° W., and not being near any known land. Its depression during thirty-six hours being only to 30.34, the gale veering to N.E., and finally S. by E. In this instance the barometer standing so high that the wind at north, was rather a contrary working of the mercury, as the north wind in southern climes tends always to its descent.
But although the high column created my surprise, I was in full expectation of the gale and its weight, as daylight broke the preceding morning in a lofty altitude, the display of clouds, in and near the zenith, being the corroid, cirrus proper, the cirro-stratus in its long horizontal lines, with hard and well defined edges, for these are Nature's grand and certain notifiers, or forewarners of her terrific and destructive performances, and to such I would call the attention of mariners, let the barometer stand and work how it may.
In the Beagle's Voyages mention is made, that all barometers do not act alike, founded of course by observing that some fall lower than others, even says the writer to tenths, to which might be added they are not equally affected by the change of weather, although they should be so. Of two that were suspended in our main cabin, it was always observed that No. 1, a barometer by Stebbing, of Portsmouth, and No. 2, maker, Charles Jones Liverpool, never acted alike, unless in a long continuance of fine weather. No. 1 rose sooner after a gale than No. 2, and its depression was slower ; No. 2 not only descended quicker but lower, and it rose slower. and in the moderating of a gale of four or six hours, what may be termed a lull, No. 2 would remain unmoved, whereas No. l would run up a tenth or more ; the descent of No. 2 was generally two-tenths lower, and four or six hours quicker than No. 1 ; and this was invariably the case, either at sea or in harbour. In meeting three vessels after a gale in which No. 1 indicated 28.28, the three barometers in the different vessels marked 28.05, being rather more than two-tenths lower. In point of value it is probable that No. 1 cost at the maker's something more than No. 2, as it was by far the most sightly article ; but in the intrinsic worth to the mariner No. 2 was worth a ship load of No. 1.
J.M. Gill, Master.