The gas meter was invented by Clegg in 1816. Since that epoch no essential modification has been made of its structure. Fig. 1 shows the principle of the apparatus, mnpq is a drum movable around a horizontal axis. This is divided by partitions of peculiar form into four vessels of equal capacity, and dips into a closed water reservoir, RR'. A tube, t, near the axis, and the orifice of which is above the level of the water, leads the gas to be measured. This latter enters under the partition, l'm, of one of the buckets, and exerts an upward thrust upon it that communicates a rotary motion to the drum. The bucket, l'mi, closed hydraulically, rises and fills with gas until the following one comes to occupy its place above the entrance tube and fills with gas in turn. Simultaneously, as soon as the edge of each bucket emerges at e, the gas flows out through the opening that the water ceases to close, and escapes from the reservoir through the exit aperture, S. The gas, in continuing to traverse the system, is thus filling one bucket while the preceding one is losing its contents; so that, if the capacity of each bucket is known, the volumes of the gas discharged will likewise be known when the number of revolutions made by the drum shall have been counted.

The addition of a revolution counter to the drum, then, will solve the problem.



The instrument, as usually constructed, is shown in Figs. 2 and 3.

The reservoir, RR' contains the measuring drum, mmmm, movable around the horizontal axis, aa'. The gas enters at E, passes at S into an opening that may be closed by a valve, and is distributed through the box, BB', which communicates with the reservoir through an orifice in the partition, hh'. This orifice is traversed by the axle, aa'. The box, like the reservoir, contains water up to a certain level, r. Through a U-shaped tube, lnl', the gas passes from the box, BB', into the movable drum, sets the latter in motion, and makes its exit at S. In order to count the volume discharged, that is to say, the number of revolutions of the drum, the axle terminates at a in an endless screw which, by means of a cog wheel, moves a vertical rod that traverses the tube, gg, and projects from the box. As the tube, gg, dips into the water, it does not allow the gas to escape, and this permits of the revolution counter that the rod actuates being placed in an external case, CC'.

The counter consists of toothed wheels and pinions so arranged that if the first wheel makes one complete revolution corresponding to a discharge of 1,000 liters, the following wheel, which indicates cubic meters, shall advance one division, and that if this second wheel makes one complete revolution marked 10 cubic meters, the third, which indicates tenths, shall advance one division, and so on. Hands fixed to the axles of the wheels, and movable over dials, permit the volume of gas to be read that has traversed the counter.

The object of the other parts of the instrument are to secure regularity in its operation by keeping the level of the liquid constant. It is evident, in fact, that if the level of the water gets below r, the capacity of the buckets will be increased, and the counter will indicate a discharge less than is really the case, and vice versa. If the level descends as far as to the orifice in the partition, hh', the gas will flow out without causing the apparatus to move. The water is introduced into the counter through f, which is closed with a screw cap, and passes through the opening shown by dotted lines into the reservoir, RR', whence it flows to the box, BB', When it has reached the desired level, it gains the orifice, r, of a waste pipe, escapes through the siphon, ruv, and makes its exit through the aperture, b', when the screw cap of the latter is removed. If, by accident, the level of the water should fall below a certain limit, a float, f, which follows its every movement, would close the valve, s, and stop the flow of the gas.

Finally a tube, tt' soldered to the lower part of the tube, lnl', and dipping into the water of a compartment, P, serves to allow the surplus water to flow out at b'. To prevent the apparatus from being disarranged upon the drum being revolved in the opposite direction, there is fixed to the axle, aa', a cam which lifts a click, z, when the rotation is regular, but which is arrested by it when the contrary is the case. - Science et Nature.