METER. An instrument for measur ing gas. When gas commenced to be used extensively, it was found necessary to have some check upon the gas-works us well as the public, as a means of calcu lating between the works and large con sumers, and indicating accurately the amount consumed. This has been, to a great extent, accomplished by the gas clock or gas-meter. The principle in the construction is simple. When a number of vessels of a certain capacity, say 1 cu bic foot, are so arranged that (without loss of gas in the interval) one after the other shall be filled by the gas in passing, and for this purpose are inverted in wa ter, into which the gas enters, just as is the case on a large scale with the gasom eter; it follows, that just its many cubic feet of gas will have passed, as there are air-vessels that have filled. If these ves sels be attached to a common axis, upon which they revolve as they fill and rise, every revolution will correspond with 4 cubic feet of gas that have passed through. In the actual gas-meter, instead of sep arate vessels, compartments of a drum of equal and known capacity are used. The drum revolves in a case more than half filled with water (dilute alcohol in winter), and is divided by 4 crooked partitions into as many chambers. The contents of each chamber are closed at the front and back by the straight sides of the drum, above, by the crooked partition, and below by the water. The tube for the admission of the gas enters at the back, and delivers into the uppermost box ; as this fills it be comes lighter, and rising, revolves on its axis until it gets above the level of the water, when it parts with the gas through a narrow slit into the space above, when the gas is carried on into the consuming pipe. The moment one chamber is emp tied, another is filled with water and placed above the pipe, which enters from the back ; it becomes filled and acts simi larly to the first, and so on, with the four. To the axis of the drum is attached a toothed wheel, which turns a hand by means of works upon a clock plate, which has generally 8 dials, indicating 1, 10, and 100 revolutions, and thus the quantity Of gas which has passed is ascertained in cubic feet.
In practice, the construction of the wet metre admits of fraud being- practised with it. If, for instance, the water level be lowered, more gas will pass through than will be registered; if the meter be tilted forward and some of the fluid drawn out, gas will pass through without being registered at all.
These objections havo given rise to the use of dry meters, in which any fluid in the box is dispensed with. In dry me ters, the gas is measured by the number of times that a certain bulk will fill a chamber capable of undergoing contrac tion and expansion by the passage of the gas. These alternate contractions and expansions of the chamber, set valves in motion, which, aided by light arms and wheels, turn the hand of a dial, as in the wet meter. The largest meter yet constructed is one by Mr. Defries, on the dry meter plan, for the registering the gas used in Covent Garden Theatre, Lon don. It is said to be very accurate in its measurements. It contains two cham bers: the upper one holds the machin ery; the lower is divided into 6 compart ments by three movable diaphragms, and 3 fixed partitions. The gas enters at the inlet pipe, whence it passes through the bottom of the meter, and fills each compartment in succession, a continuous supply is kept up by the action on the movable diaphragms, which acts on the indicating machinery by means of a very simple and ingenious contrivance that registers the consumption of gas with unerring accuracy on a plate of 6 dials and indexes, from units to millions. This meter is capable of measuring 6000 cubic feet per hour, and is to measure the sup ply of 1500 burners. It weighs 2 tons, is 16 feet in circumference, and 8 in height. The shape is a hexagon, with gothic de vices.
The wet gas-meter can be made to in dicate favorably for the gas companies, and it is more frequently in error on that side, than favoring the consumer ; the dry meter does not appear to be based on true philosophical principles, and will, in all likelihood, not hold its ground. A correct meter is still a de sideratum.