When the surface of the mercury is convex, or stands higher in the middle than at the sides, it is a sign the mercury is then in a rising state; but if the surface be concave, or hollow in the middle, it is then sinking.
In very hot weather, the falling of the mercury indicates thunder.
In winter, the rising presages frost; and in frosty weather, if the mercury falls three or four divisions, there will be a thaw. But in a continued frost, if the mercury rises, it will certainly snow.
When wet weather happens soon after the depression of the mercury, expect but little of it; on the contrary, expect but little fair weather, when it proves fair shortly after the mercury has risen.
In wet weather, when the mercury rises much and high, and so continues for two or three days before the bad weather is entirely over, then a continuance of fair weather may be expected.
In fair weather, when the mercury falls much and low, and thus continues for two or three days before the rain comes, then a deal of wet may be expected, and probably high winds.
The unsettled motion of the mercury denotes unsettled weather.
The words engraved on the scale are not so much to be attended to, as the rising and falling of the mercury; for if it stands at much rain, and then rises to changeable, it denotes fair weather, though not to continue so long as if the mercury had risen higher.
If the mercury stands at fair, and falls to changeable, bad weather may be expected.
In winter, spring, and autumn, the sudden falling of the mercury, and that for a large space, denotes high winds and storms; but in summer it presages heavy showers, and often thunder. It always sinks very low for great winds, though not accompanied with rain; but it falls more for wind and rain together, than for either of them alone.