observers to record in detail the rate at which heavy rains fall during thunderstorms. With one of these instruments, in London, on June 23, 1878, rain was ascertained to be falling for thirty seconds at the rate of 12 inches an hour, or 288 inches a day. The first pattern of this gauge was apt to be broken by frost, and therefore could be put out only in summer time. In a second stronger and more elaborate instrument (Fig. 48) the rain passes into a copper cylinder in which is a float, which rises as the rain falls. The float has a string passing round a pulley, and kept taut by a counterpoise. Therefore, when the float rises, the pulley turns. To the extremity of the axle of the pulley a hand or index is attached, which completes a revolution on a graduated dial when an inch of rain has fallen. Inside the case there is a simple wheel-work whereby another short hand, like the hour-hand of a clock, completes a revolution for 5. inches of rain. With this gauge it is therefore quite easy to read from a window the fall of rain to hundredths of an inch, and by doing this, say, every thirty seconds, the minutest detail of the fall of rain can be ascertained. This instrument is constructed by Negretti and Zambra.

There are several self-registering and recording rain gauges. For example

5. Crosley's registering rain gauge, of which the area is 100 inches (Fig. 49). Beneath the tube leading from the funnel there is a vibrating divided bucket. When one compartment of this bucket has received a cubic inch of water, that is, when 0.01 inch of rain has fallen, the bucket tips, the index advances

on the first dial, and the second bucket begins to fill, and so on indefinitely. Crosley was a gas-meter maker, and brought out his gauge first in the year 1829.

FIG. 51.-Registering part of Yeates's Rain Gauge.

6. Messrs. Yeates and Son of Dublin have designed a very ingenious electrical self-registering rain gauge (Figs. 50 and 51). The funnel is 100 square inches in area, and the measuring

bucket (the working parts of which are made of platinum alloy

with agate bearings) is

At

adjusted to turn with one cubic inch of water. each turn of the bucket electrical contact is made, and the index hand moves one division. The advantage of this instrument is that the funnel may be placed in any exposed position out of doors, while the registering part can be fixed indoors. As this apparatus is entirely self-acting, each cubic inch of water, as it is weighed and recorded, is emptied out, so that no error can arise from evaporation.

7. MM. Richard Frères, of Paris, have invented a float pattern and a balance - pattern self-recording rain gauge. In the float pattern (Fig. 52) a funnel collects the rain, which is carried by a pipe into a reservoir in which there is a float. A style, carrying a writing pen, follows the motion of the float, rising 4 inches for a rainfall of 0.4 inch. When the pen

FIG. 52-Richards' Self-recording Rain Gauge (Float Pattern).

reaches the top of a revolving drum, the reservoir empties itself automatically by means of a siphon, the float falls to the bottom, and the pen returns to zero. The siphon is started by an electro-magnet which, on the circuit of a battery being

FIG. 53.-Richards' Self-recording Rain Gauge (Balance Pattern). completed, pulls the float down and causes a sudden rise of the water-level, thereby filling the siphon. In the balance or bucket pattern (Fig. 53) the rain is led into a tipping-bucket divided into two compartments and placed on a balance. One of these compartments being under the funnel, the rain falls into it

and causes the balance to descend. A writing pen records this motion on a revolving drum. When the pen has reached the top of the drum (0·4 inch of rain), the tipping-bucket reservoir oscillates, and the water filling the first compartment is emptied into a controlling reservoir. This motion causes the second or empty compartment of the bucket to place itself under the funnel. The filling and emptying of each compartment is alternately and automatically produced, and to each of these double operations a rise and a fall of the writing pen corresponds. It may be well to mention that Mr. L. Casella, of Holborn Bars, London, E.C., is agent for MM. Richard Frères of Paris, and through him any of the automatic recording instruments of the Richard system can be obtained.

No matter what rain gauge is employed, the instrument should be firmly set in a well-exposed position, at least as far in feet from any building, tree, or high wall, as the height of that obstacle. "The angle subtended in each azimuth by the nearest obstacle, such as a building or tree, should not exceed 30°, and the true bearing of the obstacle from the gauge should be carefully measured and noted in the register" (R. H. Scott). The gauge should be placed on the ground rather than on a roof, unless in the case of a small town garden in which it is impossible to obtain a sufficient exposure. The height of the rim of the funnel should be 1 foot above the ground. This should be given in all returns of rainfall as well as the height of the gauge above mean sea-level. It is essential that the top of the cylinder above the funnel should be absolutely horizontal.

Measurement of Rain.-The rainfall should be measured at 9 A.M. daily, and the amount should be entered to the previous day, for of the twenty-four hours which elapsed since the last measurement, fifteen belonged to the previous day, and only nine to the day on which the measurement is made. The gauge must be examined daily, whether rain has fallen or not; if there is no water in the gauge a line or dash should be inserted in the register. The water is poured from the can in the interior of the gauge into the graduated