Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 1, 1802).djvu/203

179&#93; BAR Nevertheless, experience has fur- nished us with a sufficient number of facts, from which we may, with tolerable precision, ascertain the present, and predict the future state of the. surrounding element, by the practical use of the barometer. Thus, 1. The rising of the quick- silver generally presages fair wea- ther, as its falling does the contrary, or rain, snow, high winds and storms ; 2. In very hot weather, the sudden falling of the mercury portends thunder; 3. In winter, the rising indicates frost; and in frosty weather, if the mercury falls three or four divisions, there will certainly follow a thaw ; but if it rise in a continued frost, it will always be accompanied with snow; 4. When foul weather quickly suc- ceeds after the falling of the mer- cury, it will not be of long dura- tion ; nor are we to expect a con- tinuance of fair weather, when it soon succeeds the rise of the quick- silver ; 5. If, in foul weather, the mercury happens to ascend consi- derably, and continues in an ad- vancing state for two or three days successively, then we may expect also a continuance of fair weather; 6. If, in clear weather, the mer- cury falls remarkably for two or three (Jays together, before the rain sets in, it is then highly pro- bable that it will be succeeded by much rain, and perhaps high winds ; /. The unsettled motion Of the mercury indicates changeab'e weather; 8. Respefting the words engraved on the register-plate, they cannot be strictly relied upon to correspond exactly with the state of the weather; though it will in ge- neral agree with them as to the mercury rising and Jailing. These words deserve to be particularly noticed when the mercury removes BAR [i 79 from cc Changeable" upwards ; as those on the lower part should be adverted to, when the quicksilver falls from " Changeable" down- wards. In other cases, they are of no use ; for as its rising in any part forebodes a tendency to fair, and its falling to foul weather, it follows, that though it descend in the tube from Settled to Fair, it may never- theless be attended with a little rain ; and when it rises from the words " Much Rain" to " Rain," it shews only an inclination to become fair, though the wet weather may still continue in a less considerable de- gree than it was when die mercury began to rise. But if the mercury, after having fallen to " Much Rain," should ascend to " Changeable," it predicts fair weather, though of a shorter continuance than if the quicksilver had risen still higher; and so, on tire contrary, if the mer- cury stood at " Fair," and descends to " Changeable,*' it presages foul weather, though not of such dura- tion, as if it had fallen lower. These observations are founded on experience, and we are indebted for them chierly to Mr. Patrick, who has investigated this subject with considerable precision. It ap- pears from the result of these facts, that the height of the mercury is not the principal criterion for ascer- taining the probable changes of the weather, but rather the relative motion of that fluid in the tube. Hence, to enable us to judge right- ly of the impending variations, we ought to possess a correct know- ledge, whether the mercury is ac- tually rising or falling. For this purpose, the following rules, stated by Mr. Rowing, maybe of advan- tage : 1. If the surface of the mer- cury be convex, standing higher in the middle of die tube than at the N J. sides,