The opinion generally entertained that a high barometer is an indication of fine weather, and a low one a warning of bad weather, is open to exception, and an increased value would attach to the indications of the instrument in proportion as the following points are noted and allowed for:— 1. The actual height of the mercury. 2. Whether it is rising or falling. 3. The rate of rise and fall. 4. Whether the rise or fall has been long continued. The state of the barometer foretells _coming_ weather, and when the present weather disagrees with the barometer a change will soon take place. A fall of half a tenth, or more, in an hour is a sure warning of a storm, a rapid rise is a warning of unsettled weather. The barometer is generally lowest with wind from the S.W., and highest with wind N.E., or with a calm. N.E. and S.W. may be called the wind’s poles, and the difference of height due to _direction_ only from one of these bearings to another amounts to about half an inch. BAROMETER PRECAUTIONS. If vacuum suspected, cause mercury to strike top of tube. A clear metallic “click” indicates a good vacuum. A dull “thud” indicates air or moisture. In latter case return to optician, but if unable Incline _very_ gently until nearly inverted, when Air if present will ascend in a bubble into the cistern. Suspend barometer in good light out of sunshine. Let no heat of fire or lamp affect it. Let no sudden changes of temperature affect it. It _must_ hang _absolutely_ vertically. Note temperature of attached thermometer before reading barometer. Then adjust mercury in cistern to touch ivory point. Then adjust vernier and take reading _quickly_. Ascertain height above sea-level according to direction. The Storm Glass (Fig. 36) is a glass bottle, ten inches long, containing a mixture of camphor, nitre, sal-ammoniac, alcohol, and water. As “temperature affects the mixture much,” an arrangement has recently been designed in which the stem of a thermometer is immersed in the fluid, as shown at Fig. 37, thus imparting a higher value to its indications. The late Admiral Fitzroy says— “Since 1825, we have generally had some of these glasses, as curiosities rather than otherwise; for nothing certain could be made of their variations until lately, when it was fairly demonstrated that if fixed undisturbed in free air, not exposed to radiation, fire, or sun, but in the ordinary light of a well-ventilated room, or, _preferably_, in the outer air, the chemical mixture in a so-called storm glass varies in character with the _direction_ of the wind—not its force.” The quarter from which the wind or storm is blowing is indicated by the substance adhering more closely to the bottom of the glass _opposite_ to the point whence the wind or tempest arises.