and generally popular Edison chemical meter, and I will not attempt to do so.1

An electro-plating bath in its meter form as generally used, does not, however, give a dial indication, and the consumers ask for a dial indication almost invariably, unless they have already become thoroughly familiarized with Edison meters as used by many large Edison stations.

Many very ingenious and some quite successful attempts have been made to actuate a train of gears by the electro-deposition of an electrolytic bath. Thus, we have two electrodes suspended at the opposite ends of a walking-beam, as shown in Fig. 1. This

000

FIG. 1.

walking-beam is in various ways connected with a pole-changer, and as but a small portion of the current being measured, passes through the true meter (for of course almost all chemical meters are shunted) the pole-changer is not perhaps a very serious objection 2

The action of such a meter as this is obvious; we have a deposit from one electrode onto the other, until the second electrode becomes the heavier, when the beam tips and the recording device is set one notch ahead, the pole-changer is thrown over, and the deposit takes place in an opposite direction, the former plus electrode becoming the minus, and so on. This device deposits and reposits the same zinc, or rather electrode material. Again, we have a modification of the same device in the form of a wheel bearing a number of electrodes, and on the same principle setting up continuous rotation,

1. See Jenks on the Edison Chemical Meter, TRANSACTIONS, vol. vi., p. 26. 2. See also, TRANSACTIONS, vol. vi., p. 32.

error.

It should be noted, that in this first digression from the chemical meter, we at once meet with the prime factor of difficulty in all motor meter construction-that of friction, which, if uncompensated, must invariably introduce more or less serious We shall touch on this point more fully hereafter. Another form of self-registering electrolytic meter has a cathode plate suspended from a spring-balance, an ordinary sensitive spring weighing machine, and the heavier the cathode grows, so much greater is the registration of the spring indicator. This device is perhaps preferable to the reciprocating movement just described, but is limited in the capacity of the spring, and probably lacks sensitiveness to small amounts, being dependent of course solely upon the nicety of construction in the springbalance.

Mercury has at times been employed in the construction of electrolytic meters, and with at least moderate success, for with a mercury, anode and a cathode of the same or other material, a record easily measured may be obtained, and such a meter may even be made self-registering in a graduated tube or by half adozen other more or less simple means. Such are the more typical electrolytic meters. There are other similar devices which have not been mentioned, for it is absolutely impossible to deal with everything within the brief limits of a single

paper.

Another form of chemical meter formerly quite popular among inventors, depended for its registration upon the decomposition of water, generally acidulated water, and sometimes upon the decomposition of more volatile substances. This class of meter may very properly be divided under two heads :

First, are those meters simply dependent upon the measurement of the gas developed by the decomposition of water through any gas registering device. We may say that such meters are mere decomposing baths connected to a gas meter. There are some devices of merit which may be classed under this head, but the principle is probably not commercial, for we have nothing very successful of this kind in use to-day.

One of the more ingenious meters of this class provides a diagonally placed rotating wheel with pockets; the decomposition takes place directly under each pocket progressively, and as the air pocket fills with gas, the wheel rotates sufficiently to free this gas at the surface of the fluid, bringing another pocket into

place. Others have a rising and falling diaphragm like the popular gas meter, and still others, a delicately poised air fan over a minute aperture. This last device is obviously most

inefficient.

The second group of meters under this classification brings us to the thermo-meters; a typical group containing a few meters of more or less pronounced merit.

Those thermo-meters depending upon volatilization of a fluid, generally have two or more sealed bulbs partly filled with some volatile fluid, as for example, naphtha or ether. When two such bulbs are used, they have generally been mounted on a walkingbeam mechanism combined with a pole-changer; each bulb containing some kind of a rheostat or heat developing device dependent for its heat on the current passing through the meter, the two bulbs communicating with one another. The rheostat in but one bulb is in circuit. The heat developed in the rheostat in circuit, volatilizes more or less rapidly the fluid contained in this bulb, according to the current passing through it. The gas developed either passes in gaseous form into the second bulb and condenses, or else, as is more common, forces the fluid remaining by the simple increase of pressure into bulb No. 2, which at once becomes heavier and causes its end of the beam to fall. This throws the pole-changer, and the rheostat in the second bulb is thrown into action, repeating the operation as just described. To be successful, such a device must be very sensitive, and to be sensitive, the construction must be of a more or less expensive character, and so delicate as to be to a greater or less degree prohibitive. Like the walking-beam meters just described, instruments of this class have been designed with a number of bulbs mounted on a rotating wheel; the same actuating principle holding true for all such devices.

Another ingenious form of thermo-meter, no longer in any sense a chemical meter, is an instrument dependent for its action. upon the heat in a confined but circulating atmosphere. Thus a rheostat dependent for its heat upon the amount of current passing, is so arranged as to heat a body of air, which, by the peculiar construction of its receptacle, at once commences to circulate more or less rapidly, dependent upon the heat. It is obvious, that if a delicate air fan, a screw propeller in fact, be suspended over such a column of circulating air, its speed would

increase with the speed and volume of circulation. One of the most ingenious and most interesting meters that it has ever been my good fortune to see, is the Forbes meter,' constructed on this plan. But here friction is the most serious consideration; the torque obtained in this manner being necessarily small.

While the Forbes meter cannot perhaps be properly considered as a motor meter in the true sense of the word, it still must be classed as such in a certain sense, and I think it may safely be accepted as an axiom, that to be successful in practical operation, a motor meter of any kind must be of high torque, for it is only by the combination of high torque and compensated friction that accurate results can be obtained on light loads. I might say that almost any one can build a meter which will record fairly accurately on heavy loads; the difficulty is to build a sensitive and accurate meter for very light loads down to one lamp.

Another ingenious and quite positive form of heat meter consists of two metallic rods, or in some cases of two bi-metallic rods, somewhat similar to an ordinary thermostat; such meters being in fact a simple application of the thermostat principle to a recording device. Two rods of this kind may be placed vertically, one under each end of a walking-beam mechanism, the familiar pole-changing device being again brought into play to throw the current first through one rod and then through the other. The character of the walking-beam must be such, that only a slight movement is needed to actuate the recording mechanism and the pole-changer.

The method of operation of a meter of this kind is obvious; the alternate expansion and contraction of the two rods as they are thrown in and out of circuit, will occur with a rapidity dependent upon the current passing, and, as each rod lengthens, it throws over the walking-beam onto the shorter cool rod, and the same action follows from that side.

I think no comments are needed on such a device as this; it probably lacks sensitiveness to a marked degree and is open to other objections which are sufficiently apparent.

Probably better than this is the system of bi-metallic rods with one contracting and one expanding side, which bend to right

1. TRANSACTIONS, vol. v., p. 35.

and left, or up and down, with a rapidity dependent upon the strength of the current, a pole changer of course being used as before.

The method of actuating a train of gears by this system is comparatively simple, and not open to as many objections as the device just described.

I have neglected to state heretofore that the bulk of the thermo-meters are actuated on the shunt principle. It is obviously out of the question to operate a pole-changer by means of a meter, which shall break the full current passing to the lamps. As a rule, a very small portion of the total current is carried through the meter around a positive shunt. Instead of shunting the current, this device has at times been applied to alternating work by the introduction of a kind of transformer, which takes a few turns of wire in series with the lamps and transfers the energy through a secondary to actuate the meter; thus the meter is not on the lamp circuit at all, but on the independent secondary. But this intervention of induction is probably not desirable in cases of this kind.

A patent issued in the year 1889 to a Mr. Dahl, tells us of another quite unique form of thermo-meter, and this is probably the only heat meter actuated by an actual field and armature arrangement. In this instrument, the inventor provides a field of iron excited by a few series turns on the lamp circuit. The strength of the field should therefore bear a more or less definite relation to the amount of current passing through its turns. I will not comment upon how direct this relation would be. It will suffice to say that the introduction of iron in the construction of any meter of this character is probably detrimental to its accuracy to a quite marked degree. This, however, is aside from the subject in hand.

On a shaft in the meter which we are describing, is suspended a kind of armature consisting of a flat disk-like ring of iron, sup ported by a number of spokes and mounted as a wheel; in fact it is mounted on a quite ordinary shaft mechanism suspended in proper bearings. The iron portion of the wheel, rotates between the poles of the electro-magnet, or at times permanent magnet just described. We have, in fact, a disk armature rotating in such a manner as to pass between two poles of a more or less strong field. On the principle of the familiar thermo-magnetic motor, rotation is obtained in this meter by so placing coils of