The following notes are on reading and regulating a mercurial barometer (Fitzroy pattern). The dial on the face is divided into set fair, fair, change, wet, "very wet; these require no explaining. The numbers 29, 30, 31, etc., refer to the height of mercury in inches. One hand works round the dial as the mercury rises and falls; the other hand is stationary, but may be moved by a small knob below; this hand is set directly over the movable hand each day, and serves to show any change in the instrument. To regulate the barometer, it should be compared at a certain time, morning and evening of each day, with a standard barometer or with another barometer which is known to be accurate. If the readings are appreciably incorrect, open the back of the case and add or take away a drop of mercury as required; continue this treatment until the instrument reads the same as the standard.