Fig. 83.
109. Plan of Exposing Thermometers, &c.—Figure 83 is an illustration of a convenient slab for supporting thermometers in an exposed position attached to a stand (such as [Glaisher’s, described in Chapter XVI.]) for ordinary scientific observations. It has a projecting ledge, B, to carry off rain from the instruments, the slab, A, being erected vertically. The hygrometer is placed at E, with the vase of water at F. An alcohol minimum thermometer is represented at C, in the position most favourable to its certain action; and at D is shown one of Negretti & Zambra’s maximum thermometers, the position of which may be more nearly horizontal than there exhibited, although a slight depression of the bulb-end of the frame is desirable, but not necessary, as this thermometer can be used in any position.
CHAPTER XII.
INSTRUMENTS USED FOR MEASURING THE RAINFALL.
The instruments in use for measuring the quantity of rain which falls on a given spot are of very simple construction. Perhaps the simplest is:—
110. Howard’s Rain-Gauge.—It consists of a copper funnel, a stout glass or stone bottle, and a measuring glass. The bottle is to be placed upon the ground, with the funnel resting on its neck. A brass band or cylinder fixed upon the outer surface of the funnel envelops the neck of the bottle, and the pipe of the funnel extends nearly to the bottom of the bottle; so that loss by evaporation is avoided as much as possible. The receiving space of the funnel is formed by a brass ring, five inches in diameter, very accurately turned. The measuring vessel enables the observer to note the rainfall in inches, tenths, and hundredths of an inch.
Fig. 84.