is connected in shunt to the main circuit. Those parts of the armature which are immersed in the mercury are nickel plated, which is claimed to be preferable to amalgamated contacts. In a similar meter shown to me at the same time by the inventor, Professor Perry, the concentric poles of the electro-magnet had a fluted surface so that the toothlike projections of the external pole were placed opposite to similar projections of the internal pole. [See Fig. 3.] The armature would thus rotate in magnetic field of varying intensity, the induced currents genera ted during rotation in the armature increasing the "drag" which is a very desirable feature, as Mr. Haskins has pointed out. Professor Perry also proposes to immerse his armature almost entirely in mercury, so that the surface tension and friction connected therewith, will only exist where the shaft of the arma о FIG. 3.-Perry's Meter. Horizontal cross-section of field magnets. ture emerges from the mercury. (Mercury to be used for the purpose of making contact for large currents does not seem to me to be a desirable and practical feature of a meter under any circumstances.) Returning to the Teague meter, I was informed by the maker, that its greatest number of revolutions does not exceed 25 per minute, which would be a very good feature of this meter. The speed curve given to me and represented in the diagram, Fig. 4, represents most likely the meter at its best, otherwise it would not have been made public. This curve is taken from a meter which is to register from half an ampere up to 25 amperes. The following table is compiled from the speed curve, in which the heavy line indicates rising, the dotted line falling current. The readings were taken at a temperature in the case of 25.5 C. Mean of total number of observations 2.755 Watt-hours per turn. 2.67 46 This meter shows bad frictional errors for the lower ranges, and is not reliable below three amperes, that is below 12 per cent. of its maximum capacity. Taking the useful range, from 3 to 25 amperes, this meter is right within about 2 per cent., the error being in this case mostly in favor of the consumer apparently, although the percentage error for rising and falling current would to some extent have an equalizing effect. It would however, be only a question of time and of a very short time at that, when the error would be entirely against the consumer, since the frictional errors in this type of meter must increase very rapidly. It is quite a different thing to criticize an instrument from a laboratory test, and from tests made in actual practice extending over a longer period. The Board of Trade of London seems then to be satisfied with an accuracy as exhibited by this meter; I do not think we would be satisfied with it in this country. Mr. Haskins mentions in his paper, "that the watt is the only true unit for the measurement of electricity by meter." In principle I agree in this completely with Mr. Haskins, but the general public seems to think otherwise. This very day I was informed by a gentleman from one of the Edison illuminating WATT-HOURS PER TURN companies, that his customers want their bills in ampere, or rather lamp hours. As an advantage of this way of rendering the bills they claim, that they know how many amperes a lamp takes, and if they wish to check their meters they can note the number of hours and the number of lights which they use, and thus check their bills. If the bill was rendered in watts or kilowatts, 99 per cent. of the customers would be entirely at sea as to what it meant, and therefore, they claim would not have the means of making a rough check on the meter. At the present state of the meter question, I do not know whether it is so very desirable for the producer to have the customer get a check on the meter. In most of the motor meters, I think, though I am not so very familiar with this subject, the energy consumed is considerable, and I have heard frequently in connection with the Thomson meter, that in comparison with the chemical meter, it is decidedly inferior so far as the energy consumed is concerned. 21 22 23 24 AMPERES FIG. 4. The mentioning of the use of graphical registering devices reminds me of a patent which I noticed only recently in which puncturing by means of a spark passing from the pointer to a metallic drum is made use of. I have serious doubts whether this would be practical, since I should certainly think that the static charge on the pointer and on another conductor in its neighborhood, would seriously interfere with the indications of the instrument. I should not think that the winding up of a clock meter, (and I am convinced that the difficulties are so far best solved in clock meters) is a very serious objection. We have to send somebody to read the meter and it would be just as well for the man to wind it up at the same time. Mr. Wolcott has already touched upon the question of the influence of self-induction in wattmeters for alternating current, inasmuch as they might be claimed to give correct readings for very different frequencies. In watt measurements in inductive circuits, we may be able to reduce such errors to a minimum for a special case, but not for all possible cases. The construction of a wattmeter equally well adapted for the measurement of energy in continuous and alternating current circuits presents very great difficulties, and I am satisfied, that at the present time we are not in possession of a meter which will do this satisfactorily. It would be interesting to hear more from Mr. Haskins about the efficiency of such meters as have come under his observation. MR. FRED. W. TISCHENDOERFER :-In regard to Mr. Haskins's conclusion about motor meters, I would like to call your attention to a recording wattmeter invented by Mr. Hummel, which fulfills all the conditions mentioned as necessary for an accurate and sensitive apparatus. These motor meters I refer to, have been in practical use since 1886, and were exhibited at the Frankfort exposition. In Schuckert and Company's catalogue, including their exhibited machines and apparatus, the plates and description of this direct-reading meter are given. The armature and field have no iron. The field is in the main circuit, and the armature, which carries a commutator with a few segments, is connected in derivation. To balance the mechanical friction, and at the same time to start the motor at a small percentage of the maximum current, for which the instrument is built, a fine wire field coil, connected in shunt to the line, is provided for. For damping the speed of the motor, the armature shaft carries a copper disk which revolves between the poles of an electro-magnet, the latter being also in shunt to the line terminals, thus securing a constant damping coefficient. The sensitiveness of the apparatus is such, that readings are made at one per cent. of the maximum current the meter is made for, and the exactness of the apparatus, found by many tests, gives a maximum error of less than one and a half per cent. The patent of this recording wattmeter dates from the year 1887. I would like to show the plates to any one interested in it. MR. A. E. KENNELLY:-In regard to the question whether a meter should be made an ammeter or a wattmeter, I have the honor to differ with the author to some extent. When power is delivered, when a motor is operated, from a continuous current circuit, a wattmeter is indeed preferable, since if the pressure falls below the normal, the consumer is deprived of the full measure of power to which he is entitled, but in electric lighting the case is so different that surely a different consideration applies. The consumer seeks illumination, and not power. He is indifferent to the amount of power absorbed by his lamps, when the terms of his contract have once been decided. If the illumination from an incandescent lamp varied directly with the voltage, then indeed it might be desirable to record the volts and amperes conjointly, but as no such simple relationship obtains, the necessity for a wattmeter seems to disappear. All the recording ammeters in use to day are merely lamp counters, and the charge is usually based simply upon the lamp-hour and not upon the watt-hour. The necessity for regulating the voltage is forced upon the central station, partly owing to the exces sive lamp breakage that would result from too high a pressure, and partly because the consumers complain when the illumination is not up to the standard. If The important question which has been raised concerning the applicability of meters to alternating current, and to continuous current circuits, without a change in their constants, is a very important one and depends almost wholly does it not?-upon the amount of non-inductive resistance, which is necessarily in one or the other circuit. If the field, say as in the Thomson meter, is in the direct circuit of the lamp, then the armature, we will suppose, is in shunt, and the armature must have a certain inductance. there is no iron in the armature, then that inductance can be quite appreciable, provided that the non-inductive resistance in the circuit is so large that the impedance of the two in series shall not be more than, say, one per cent. greater than the simple resistance to the continuous current, and knowing the inductance and the frequency, I think it will be found that a considerable margin is allowed in this way for meters not employing iron. Mr. C. R. VAN TRUMP:-Regarding what Mr. Kennelly has said respecting a motor meter or a watt-meter, as a central station engineer I beg to approve, and to further say that I cannot see that the meter should be the exception in the case. In fact having operated a great number of Edison chemical meters, and recently taken up the Thomson meter, the wattmeter which has been so ably described. I have put the chemical meter, the ampere-meter, on the motors, and the watt-meter on the lights. We are operating a great many cranes, quite large cranes, all the way from 10, 15, 20 and 25 tons. In one case the factory is about a mile away from the station, and operated entirely by electricity. Ordinarily the average load on the cranes, perhaps, would not be over five horse-power for a whole day, but at times the operator will throw on as much as 50 or 60 horse-power. Now from a central station point of view, are we to put an investment of copper down there to keep his pressure up to the normal, or are we to put an amperemeter on, and charge him with the loss in the line, which would occur when he put enormous loads on the mains at a considerable distance from the station? It is merely a question of who is to pay for the drop, the customer or the central station, supposing of course that the line is of ample capacity for the normal load. We think it should come on the consumer. One feature that I have found in looking into, and selecting the Thomson meter is just the question of what the variation is, under different loads which was brought up in the discussion referring to a foreign meter, and I would like to know if it is possible, just what the |