meter, revolve with the same and transfer the water as already described.

The Sanders and Donovan meter is provided with a compensating hollow metallic float, accurately balanced on pivots within the front portion of the meter case, and

independent of the action of the instrument; the action of this arrangement is exceedingly simple, for, according as water is added to or withdrawn from the meter, the float rises or sinks in proportion, thus always maintaining a constant water level.

The most accurate method of insuring a constant waterline in the consumers' meters, however, is by the employ

ment of the Warner and Cowan patent drum, whereby the drum itself is so constructed as to automatically correct its registration for any fluctuation in water level. This result is brought about by forming a second and smaller drum concentric with the larger one, but having its partitions placed in the opposite direction. Its capacity is such that

the exact excess of gas passed beyond what is registered with any water level below the true one, is returned by it to the inlet to be re-measured.

Meters constructed upon this principle register exactly the quantity of gas flowing through them under all variations of water level. Figs. 55, 56, show the Warner and Cowan drum as just explained.

The dry meter is shown in figs. Nos. 57, 58, 59, as manufactured by Messrs. Cowan and Co., of West

minster. The instrument consists of an outer case which is divided by a horizontal partition into two compartments, the upper one containing the valves which convey the gas into and from the respective measuring chambers; the

lower compartment is subdivided by the vertical partition shown in the side view, to which are attached two flexible chambers. There are thus formed four distinct chambers viz., the interior of the flexible chambers, and their exteriors, or in other words, the spaces the flexible chambers move through, all being in communication with their respective ports of the slide valves

described later on.

Each of the flexible chambers is formed by a large disc supported and guided by what is known as a "flag piece" and guide, which allow it to pass with freedom through the desired distance, and keep it always in the same plane. A flexible leather band hermetically secured to the disc as well as to a ring soldered to the central partition completes the flexible chamber.

The gas on entering one of the flexible chambers expels an equal quantity of gas from the outer chamber to the burners, and when

FIG. 53.

the disc passes through a certain distance, the position of the valve is changed. The action is then reversed, the gas now entering the outer chamber and expelling a like quantity from the interior of the "bellows." The reciprocating motion given to the disc as the chambers inflate and collapse is conveyed to the valves through what are called "tangent arms," which are attached to another arm

P

fixed to the crank and called the "tangent" in the upper or valve chamber, and by means of suitable gearing works the valves, and also causes the index wheels to revolve. The valves fig. 59, are placed over each measuring chamber, and are similar to the slide valves of a steam-engine, having three ports which communicate with the inside and outside of the measuring chambers and the meter outlet.

The action of the instrument is briefly as follows:-The gas on entering one of the flexible chambers, say No. 2, the disc will be caused to move through a certain distance expelling a like quantity of gas from chamber No. 4 equal to that entering chamber 2, and when the diaphragm is distended to the required degree, the position of the cover of the valve is changed. The gas then enters chamber No. 3, expelling that from No. 1 until the disc nearly touches the ring, when the flexible chamber will be collapsed,