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116 THOMPSON'S COAST PILOT. depend rather on the rising and falling of the mercury, than on its standing at any particular height. When the mercury is as high as « fair,"? and the surface of it is concave (which is the case when it be- gins to descend, ) it very often rains ; and, on the contrary, when the mercury is opposite "rain," and the surface convex (which is the case when it begins to ascend, ) fair weather may be expected. These circumstances not being duly attended to, may be said to be the principal cause of many people not having a proper confidence in this instrument. : | * For sea service, it would be as well to read off the barometer at least three times a day, viz.: at8 A. M,, noon, and 8 P. M.; and oftener if bad weather. | , | In Europe, if the alteration in the quicksilver should be in as great a proportion as six-tenths of an inch to twenty-four hours, sudden but not lasting changes of weather may be expected. If the alteration should be gradual, probably in the proportion of two or three-tenths to twenty-four hours, the weather indicated will be likely to last. iC One-fifth of the variation of the barometer in any climate may be considered as an indication of sudden change, © 3 } : If wind should follow rain, the wind may be expected to increase, Rain following wind is likely to lull it, and the wind may be ex- pected to abate. : Explanation of the Aneroid Barometer. The graduation and figuring on the dial represents the perpen- dicular scale. of the Mercuriai Barometer. The falling of the Barometer is understood to be the passage of the long or steel index from the higher to the lower number of figures, which movement comes under the same atmospheric change in which the mercury passes over part of its scale. The short pointer is simply a register, and is only movable with the fingers, to be placed over the steel index, thus enabling the observer to see more readily any movement of the index.