and the position of the valve cover is changed. The gas enters the chambers in succession, receiving and expelling continuously so long as any supply from the instrument is required. The complete action of distention and collapse is transmitted to the index as previously described, and the gearing of the index is arranged according to the capacity of the chamber when fully inflated.

PENNY IN THE SLOT METERS.

METERS.

PREPAYMENT GAS

A considerable impetus has within the last few years been given to the consumption of gas by the invention of the penny in the slot prepayment meter.

Gas is probably one of the most important of the many commodities for the delivery of which automatic mechanism has been devised.

The system, as applied to gas, is not only useful to the public, but it also secures to gas companies and corporations a new source of revenue free from the risk of bad debts. In the United Kingdom alone there are hundreds of thousands of householders who do not burn gas, and of these a large proportion, especially in manufacturing centres, purchase their light, whether oil or candles, in small quantities, and cannot be persuaded to adopt gas because of their disinclination or inability to meet the payment of periodical gas bills. The prepayment system, in which penny in the slot prepayment meters are employed, entirely removes this difficulty because it enables the consumer to purchase at pleasure a pennyworth of gas just as he would buy oil to the same value.

When once such a meter is fixed in a house it generally remains there permanently, no matter how many changes of tenancy may occur, or how often; as each successive tenant who finds such a convenient meter in his home

readily takes to the idea and patronizes the penny in the slot meter instead of the oil seller.

Of the many penny in

the slot meters in the market, those of Messrs. Cowan and Co. enjoy a well deserved reputation. Messrs. Cowan's

A distinctive feature of these meters is the priceadjusting mechanism by means of which the gas company's inspector can readily adapt the meter in situ to a change

FIG. 61.

meters are constructed on the most reliable and approved principles, and give every satisfaction both to the consumer and to the gas company.

in the price of gas by altering the position of a pointer on a graduated scale which is under seal.

Fig. 60 shows one of Messrs. Cowan's dry meters with penny in the slot attachment, and fig. 61 the mechanism of the same, of which the following is a description:

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By turning to the right the handle fixed on the shaft a, the cam в presses against the left-hand bearing of box c c, by which it is moved forward with the pusher attached to it. If the movement of the handle be continued, the cam next presses against the right-hand bearing of the box c c, and thus draws back the pusher. No other effect is however produced, unless a penny is dropped into the slot E, the interposition of which between the pusher and the coin carrier D brings the latter into action, and carries the pawl F first forward, then backward, when the penny is released and drops into the cash box.

"By these operations the prepayment wheel & is moved partly round, and the number of feet which has been paid for by the penny is indicated by the long pointer on the dial. Successive pennies may, if convenient, be put in, but no more than 450 feet of gas can be prepaid at one time.

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A pin fixed at the back of the wheel & closes a valve on the inlet of the meter when the long pointer reaches zero. The consumer will have due warning before the supply of gas which has been paid for is exhausted, as the valve will gradually close during the consumption of the last five feet.

"The wheel G, when moved round by the pawl F, is released from the index gearing, but resumes contact therewith when the pawl recedes, and thus records in concert with the ordinary index the quantity of gas passed through the

meter.

"Price Changing. It will be obvious that with coin. meters provision must be made whereby the mechanism can be adjusted easily and in situ to meet changes in the price of gas.

"The extent of the movement given to the prepayment wheel & by the pawl depends on how much of the 'travel' of the pawl is allowed to operate on the wheel. The priceadjustment platform н (the position of which is determined by the setting of the pointer I in relation to the scale J) supports the pawl off the teeth of the wheel during more or less of the movement the pawl has. If, therefore, the adjustment platform be well forward, the movement of the pawl will produce comparatively little effect on the wheel; but if the platform be so placed that the pawl almost immediately gears into the wheel, the wheel's movement will in that case be almost equal to that of the pawl. The pointer I moves and fixes the platform, whilst the scale determines the position in which the pointer is to be fixed, and this is made to suit the price of gas in operation at the time."

THE STATION METER.

The Station Meter, as its name implies, is employed to register the amount of gas produced on the works, and is always of the "wet" description. It is in principle the same as the consumer's wet meter, although differing from the latter in a few minor details of construction.

Station meters of small dimensions are generally cylindrical; those of a larger capacity are usually made square, and frequently the outer case is very ornamental. The inlet and outlet pipes of station meters are at the back of the instrument, the inlet pipe being in the centre. The index dial is fixed in the front in the centre; the float which regulates the water-line in a consumer's meter is not employed, the water-line being indicated by a glass gauge fixed outside the instrument.

The capacity of a station meter for a works of a given size is governed by the maximum make of gas per hour, and it is requisite to see that the speed of the drum does