in the paraffin until it began to solidify, so that the pores were completely filled, and the wood at the outside covered with a layer of paraffin. In consequence thereof, nothing was noticeable when touching one terminal. If, however, the connecting wires between transformer and electrodes were laid on the table, from either electrode small sparks could be drawn by the finger. But still the results were exactly the same, as was to be expected. Now with regard to the discrepancies noted with air in Table XV, I entirely agree with Prof. A. Macfarlane, that the shape of the electrodes has a considerable influence, especially in a certain range, and have therefore excluded all the tests with pointed electrodes, and brought only some tests with balls as electrodes, without laying great stress upon them. I cannot, however, accept the influence of the shape of electrodes as explanation of the discrepancies, because in this case the differences should be greater for greater sparking distances, and the different curves converge toward each other at small sparking distances, while rather the opposite is the case. Calculating the curves of electrostatic force between the elec trodes shows, that even if the distances of the plates is equal to their radius, the distortion of the field is not yet so great, and in agreement herewith I found that even at a sparking distance of 2.2 cm. the disruptive discharge took place about as often near the centre of the plates as at their edges, so that this can not account for the discrepancies, which amount to over 100 per cent. between the different observers. Besides, if we cancel the tests made at greater sparking distances, the tests up to V- 10,000 volts alone, already give the parabolic curve. The agreement found with liquid dielectrics-which are known to have a very small dielectric hysteresis, and the disagreement of the tests made with air-which has a very large dielectric hysteresis rather point to an influence of dielectric hysteresis upon the sparking distance, and once more make the application of tests made under conditions where dielectric hystersis is absent, upon the alternating practice of suspicious value. The values calculated from Prof. Macfarlane's formula agree with the parabolic formula also, δ 19.1 V1.13 V2 with anaveage difference of .011 cm., or about 4 per cent. With regard to the extrapolations from my empirical formula, they certainly claim no reliability whatever, an empirical formula being reliable only within the range covered by the tests. I have given the potential calculated for a lightning stroke merely as a curiosity, of interest only in so far as it gives a very much lower value than former extrapolations of this kind, and therefore is perhaps somewhat nearer the truth than the former values, of 5,000,000,000 volts, etc. It is of interest, however, to note, that in the E. Thomson high-frequency transformer a sparking distance of about 2 metres has been reached, which according to my formula would correspond to about 400,000 volts, while from the ratio of transformation the E. M. F. has been estimated to about half a million volts. Furthermore, comparative tests of the sparking distance in air and in oil (A. A. Campbell, London Electrician) gave: 2 inch oil equivalent 7.875 inch air. extrapolating for air by means of the parabolic formula, gives for that is, the sparking distance in oil is nearly proportional to the potential, a result which is in agreement with tests made at lower potential difference, and thereby confirms the parabolic airformula to a certain extent. [REMARKS BY DR. J. B. WILLIAMS, AT MEETING OF MARCH 21, 1893.] DR. WILLIAMS:-Mr. President: Before the meeting closes I would like to say a word or two; for it is evident that I have been misunderstood-probably from not having been sufficiently explicit both to my remarks on electrostatic testing, at the last meeting, and to the statements made in my paper on "Oil vs. Air as an Insulating Medium," which was read at the general meeting June 8th, 1892. At the commencement of my paper, (p. 601 of the Transactions) I say, "The relative powers of the oils and air to resist disruptive discharges, and also to insulate alternating currents, will not be considered at this time, as the writer proposes to reserve those subject for a future paper." Thus it will be seen that my statements were made with reference to direct currents only. During the discussion at the February meeting, as I began by referring to direct currents, I supposed that it would be understood that my remarks would be confined to the consideration of electrostatic tests, with respect to direct currents. I should not like to be placed on record as one who does not know the difference between the values of the oils and the air as insulators for alternating currents; nor as one who claims that the electrostatic tests heretofore exhibited or described are suitable for insulated conductors, intended to convey alternating currents. AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS. New York, March 21st, 1893. The seventy-fifth meeting of the Institute was held this date at 12 West Thirty-first Street, and was called to order at 8.30 P.M., by President Frank J. Sprague. THE SECRETARY-At the dinner of the Institute, which took place last May, on the occasion of the Annual Meeting, it was voted that an annual dinner be made a regular feature of the Institute, and in accordance with that voted the Council has today appointed Messrs. Phelps, Hamilton and Pickernell as a committee on the dinner to take place on the occasion of the Annual Meeting May 16th. At the Council Meeting this afternoon the following Associate Members were elected : Everett, Washington. CHISM, GEORGE F. Standard Engineering Company of ELY, WM GROSVENOR, JR., Edison General Electric Co., 226 Union St.. Schenectady, N. Y. GOLDSBOROUGH, WINDER E. Adjunct Professor of Electrical HARTMAN, HERBERT T. Assistant Engineer, Canadian Gen- HEATH, HARRY E. KEILHOLTZ, P. O., MACKIE, C. P. Chief Draughtsman, Eddy Electric Superintendent, Endorsed by Leo Daft. Chas. H. Davis. John W. Howell. T. D. Lockwood. V. M. Berthold. I. H. Farnham. Frederick Bedell. Edw. L. Nichols. Ernest Merritt. Harris J. Ryan. E. L. Nichols. Harold B. Smith. J. H Vail. Chas. Hewitt. A. E. Winchester. H. S. Rodgers. Wm. R. C. Corson. Ralph W. Pope. Cary T. Hutchinson. T. C. Martin. Joseph Wetzler. U. S. Electric Lighting Co., H. L. Webb. Joseph Wetzler. T. C. Martin. MCCLUER, C. E. Superintendent, First District, So. MOTTRAM, WILLIAM T. M. Electrical Engineer, New Or- ROBERTSON, A. C. SPENCER, THEODORE STORRS, H. A. ZIMMERMAN, L. J. Total, 14. G. A. Hamilton. F. A. Pickernell. Thos. D. Lockwood. Wm. J. Hammer. Francis R. Upton. Oscar T. Crosby. M. J. Wightman. President, The A. C. Robertson H. Bergholtz. Ralph W. Pope. John C. Lee. H. V. Hayes. D. Lockwood. Professor of Electrical Engineering, Geo. A. Hamilton. New York City. Geo. M. Phelps. F. A. Pickernell. Townsend Wolcott. A. A. Knudson. Jas. B. Williams. Present-Messrs. W. B. Vansize, Chairman, E. T. Birdsall, G. A. Hamilton THE PRESIDENT-I take pleasure in announcing that the paper of the evening is by Dr. Charles E. Emery on "The Cost of Steam Power produced with Engines of different types under Practical Conditions; with Supplement relating to Water Power." Dr. Emery needs no introduction to his associates; he has been for a long time one of the leading members of the American Society of Mechanical Engineers, and a Vice-President, and is one of the best known steam experts in the United States. That he should after going through the ordeal of attaining that enviable position, have taken up electrical studies and become a member of the Institute is, I think, a matter for congratulation. The paper which he will read to-night is on a subject elaborated some years ago by him in a paper of now international imporI am sure that those who hear it will be fully impressed with the results at which Dr. Emery has arrived. tance. [Dr. Emery then read the following paper : |