The Committee regret that the insulation of some of the coils referred to in their last Report, which had been selected for the new standards of resistance, as defined by the resolutions adopted at Edinburgh, has proved defective. Traces of acid have been discovered in the paraffin with which the coils were filled. The two one-ohm standards of the Association,1 as well as two of the one-ohm standards of the Board of Trade, were found in January last to have so low an insulation resistance between the coil and the case as to be useless.

2

Thus the labour spent in the testing of these coils has been wasted; much of it will need to be done again. The insulation of some of the other standard ohm coils is not satisfactory. The single ohm standards have therefore been remade, and the others are being refilled with carefully selected paraffin. The original B.A. units have not, so far as comparisons between them can show, changed their values during the year, and one set of new ohm standards also has shown no sign of change.

The Committee print, as an appendix to the Report, the report of the proceedings at the International Congress at Chicago, presented to the Secretary of State at Washington by the American delegate to the Conference.

During the year Professor J. V. Jones has determined, by the aid of his Lorenz apparatus, the absolute resistance of certain wire coils of about 1 ohm. These have been compared with the standards of the Association by the Secretary. An account of these experiments is contained in Appendices II. and III. The resistance standards of the Association have been compared with those of the Board of Trade by Mr. Rennie and the Secretary. Details of this comparison will be found in Appendix IV., while in Appendix V. is given, by Mr. E. O. Walker, an account of a comparison between five coils belonging to the Indian Government, which have been for twenty-four years in India, and Dr. Muirhead's standards. Mr. Fitzpatrick has continued his work on the specific resistance of copper, and has drawn up a table (see Appendix VI.) reducing to the same units experimental results recently obtained by various observers. Appendix VII. contains the Final Report of the Electrical Standards Committee of the Board of Trade and the Order in Council relating to Standards for Electrical Measurement.

In consequence of the difficulty met with in the insulation of some of the coils, it was thought well to defer the purchase of other coils for which the grant of 251. was obtained last year. The Committee are of opinion that it is desirable to complete their set of standards by obtaining from Germany certified copies of the standards of the Reichsanstalt. They recommend, therefore, that they be reappointed, with the addition of the name of Mr. Rennie, and with a grant of 251.; that Professor G. Carey Foster be Chairman and Mr. R. T. Glazebrook Secretary.

APPENDIX I.

Report of the Action of the International Electrical Congress held in Chicago, August 1893, in the Matter of Units of Electrical Measure.

WASHINGTON, D.C.: November 6, 1893. THE HON. W. Q. GRESHAM, Secretary of State, Washington, D.C. SIR, The undersigned, having been designated by you on May 12, 1893, as delegates to represent the United States in the International

Report, 1893, p. 129.

2

Ibid., 1892, p. 134.

The

Electrical Congress to be held in August at Chicago, beg to submit herewith a brief report showing the definitive action of said Congress in the matter of defining and naming units of electrical measure. consideration of this important subject was left to what was known as the Chamber of Delegates' of the Congress, consisting only of those who had been officially commissioned by their respective Governments to act as members of said Chamber. After conference and correspondence with the leading electricians of Europe, it had been agreed that the maximum number of such delegates to be allowed to one nation should be five, and this number was allotted to the United States, Great Britain, Germany, and France. Other nations were allowed three or two, and in some instances one.

Delegates present and taking part in the discussions and action of the Chamber were as follows:

Representing the United States.

Professor H. A. Rowland, Johns Hopkins University, Baltimore, Md. Dr. T. C. Mendenhall, Superintendent of U.S. Coast and Geodetic Survey, and of Standard Weights and Measures, Washington, D.C. Professor H. S. Carhart, University of Michigan, Ann Arbor, Mich. Professor Elihu Thomson, Lynn, Mass.

Dr. E. L. Nichols, Cornell University, Ithaca, N.Y.

Representing Great Britain.

W. H. Preece, F.R.S., Engineer-in-Chief and Electrician, Post Office, England; President of the Institution of Electrical Engineers, London. W. E. Ayrton, City and Guilds of London Central Institution, Exhibition Road, London.

Professor Silvanus P. Thompson, D.Sc., F.R.S., Principal of the City and Guilds Technical College, Finsbury, London.

Alex. Siemens, 12 Queen Anne's Gate, Westminster, London, S.W.

Representing France.

E. Mascart, Membre de l'Institut, 176 Rue de l'Université, Paris. T. Violle, Professeur au Conservatoire des Arts et Métiers, 89 Boulevard St. Michel, Paris.

De la Touanne, Telegraph Engineer of the French Government, 13 Rue Soufflot, Paris.

Edouard Hospitalier, Professeur à l'École de Physique et de Chimie industrielle de la Ville de Paris; Vice-Président de la Société internationale des Electriciens, 6 Rue de Clichy, Paris.

Dr. S. Leduc, 5 Quai Fosse, Nantes.

Representing Italy.

Comm. Galileo Ferraris, Professor of Technical Physics and Electrotechnics in the R. Museo Industriale, Turin, Via Venti Settembre 46.

Representing Germany.

H.E. Hermann von Helmholtz, Präsident der physikalisch-technischen Reichsanstalt, Professor a. d. Universität, Berlin, Charlottenburg bei Berlin.

Dr. Emil Budde, Berlin N.W. Klopstockstrasse 53.

A. Schräder, Regierungsrath, Mitglied des kaiserl. Patentamts, Berlin. Dr. Ernst Voit, Professor an der technischen Hochschule, München, Schwanthalerstrasse 73-3.

Dr. Otto Lummer, Mitglied der physikalisch-technischen Reichsanstalt, Charlottenburg, Berlin.

Representing Mexico.

Augustin W. Chavez, city of Mexico.

Representing Austria.

Dr. Johann Sahulka, Technische Hochschule, Wien.

Representing Switzerland.

A. Palaz, Professeur, Lausanne.

René Thury, Ingénieur, Florissant, Genève.

Representing Sweden.

M. Wennman, Byråchef i Rougle Telegrafstyrelsen, Stockholm.

Representing British North America.

Ormond Higman, Electrician, Standards Branch, Inland Revenue Department, Ottawa.

His Excellency Dr. H. von Helmholtz was made Honorary President of the Congress; Dr. Elisha Gray, of Chicago, was Chairman of the General Congress; and Professor H. A. Rowland, of Baltimore, was President of the Chamber of Delegates.

Meetings of the Chamber continued during six days, at the end of which its members unanimously agreed in the adoption of the following resolution :

:

Resolved, That the several Governments represented by the delegates of this International Congress of Electricians be, and they are hereby, recommended to formally adopt as legal units of electrical measure the following: As a unit of resistance, the international ohm, which is based upon the ohm equal to 109 units of resistance of the C.G.S. system of electro-magnetic units, and is represented by the resistance offered to an unvarying electric current by a column of mercury at the temperature of melting ice 14.4521 grammes in mass, of a constant cross-sectional area and of the length of 106.3 cm.

As a unit of current, the international ampere, which is one-tenth of the unit of current of the C.G.S. system of electro-magnetic units, and which is represented sufficiently well for practical use by the unvarying current which, when passed through a solution of nitrate of silver in water, and, in accordance with accompanying specifications,' deposits silver at the rate of 0·001118 of a gramme per second.

In the following specification the term silver voltameter means the arrangement of apparatus by means of which an electric current is passed through a solution of nitrate of silver in water. The silver voltameter measures the total electrical quantity which has passed during the time of the experiment, and by noting this time the time average of the current, or, if the current has been kept constant, the current itself, can be deduced.

In employing the silver voltameter to measure currents of about one ampere the following arrangements should be adopted :

The kathode on which the silver is to be deposited should take the form of a

As a unit of electro-motive force, the international volt, which is the electro-motive force that, steadily applied to a conductor whose resistance is one international ohm, will produce a current of one international ampere, and which is represented sufficiently well for practical use by 1999 of the electro-motive force between the poles or electrodes of the voltaic cell known as Clark's cell, at a temperature of 15° C., and prepared in the manner described in the accompanying specification.1

As a unit of quantity, the international coulomb, which is the quantity of electricity transferred by a current of one international ampere in one second.

As a unit of capacity, the international farad, which is the capacity of a condenser charged to a potential of one international volt by one international coulomb of electricity.

As a unit of work, the joule, which is equal to 107 units of work in the C.G.S. system, and which is represented sufficiently well for practical use by the energy expended in one second by an international ampere in an international ohm.

As a unit of power, the watt, which is equal to 107 units of power in the C.G.S. system, and which is represented sufficiently well for practical use by the work done at the rate of one joule per second.

As the unit of induction, the henry, which is the induction in a circuit when the electro-motive force induced in this circuit is one international volt, while the inducing current varies at the rate of one ampere per second.

The Chamber also voted that it was not wise to adopt or recommend a standard of light at the present time.

A more complete report of the operations of the Chamber will shortly be forwarded. This brief résumé of its definite action in reference to the matter of units is now submitted to facilitate the prompt dissemination among representatives of foreign Governments of the important results of a congress of whose success and fruitfulness the United States may justly be proud.

H. A. ROWLAND.

T. C. MENDENHALL.
H. S. CARHART.

ELIHU THOMSON.
E. L. NICHOLS.

platinum bowl not less than 10 centimetres in diameter and from 4 to 5 centimetres in depth.

The anode should be a plate of pure silver some 30 sq. cm. in area and 2 or 3 mm. in thickness.

This is supported horizontally in the liquid near the top of the solution by a platinum wire passed through holes in the plate at opposite corners. To prevent the disintegrated silver which is formed on the anode from falling on to the kathode, the anode should be wrapped round with pure filter paper, secured at the back with sealing-wax.

The liquid should consist of a neutral solution of pure silver nitrate, containing about 15 parts by weight of the nitrate to 85 parts of water.

The resistance of the voltameter changes somewhat as the current passes. To prevent these changes having too great an effect on the current, some resistance besides that of the voltameter should be inserted in the circuit. The total metallic resistance of the circuit should not be less than 10 ohms.

A committee, consisting of Messrs. Helmholtz, Ayrton, and Carhart, was appointed to prepare specifications for the Clark's cell. Their report has not yet been received.