Page:Small-boat sailing; an explanation of the management of small yachts, half-decked and open sailing-boats of various rigs; sailing on sea and on river; cruising, etc (IA smallboatsailing01knig).pdf/234

 weather is taking a change for the worse. It is true that these rules hold good generally; but one would soon come to grief if one relied implicitly upon them when making a long coasting voyage with a small yacht. As a matter of fact, a rising glass, though usually indicating fine weather, is, in certain circumstances, the sign of a strong gale of wind. To read the barometer's warnings accurately requires a careful study of the meteorological conditions; and every yachtsman should provide himself with one of the handbooks published on this subject.

A barometer merely measures the weight, or pressure, of the air, and shows by its rising and falling whether the pressure is increasing or diminishing. The air naturally has a tendency to flow from a region where the pressure is greater to a region where it is less, producing a wind in that direction. Consequently, if the glass stands steadily for some time at what is its average height in that portion of the globe (in England the average height of the glass, at sea-level, is about thirty inches) it is a sign that no great atmospheric changes are taking place, the pressure being evenly distributed, and that, therefore, there will be but moderate winds and settled weather. On the other hand, a considerable rise or fall (more especially the latter) of the glass, above or below the average height, indicates a great unevenness in the atmospheric pressure, and hence gales may be expected to restore the