to provide for the election of foreign and domestic members, the division into classes, and all other matters needful or usual in such institution, and to report the same to Congress. SEC. 3. And be it further enacted, That the National Academy of Sciences shall hold an annual meeting at such place in the United States as may be designated, and the Academy shall, whenever called upon by any Department of the Government, investigate, examine, experiment, and report upon any subject of science or art, the actual expense of such investigations, examinations, experiments, and reports to be paid from appropriations which may be made for the purpose, but the Academy shall receive no compensation whatever for any services to the Government of the United States. Approved, March 3, 1863. AN ACT to amend the act to incorporate the National Academy of Sciences. Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That the act to incorporate the National Academy of Sciences, approved March third, eighteen hundred and sixty-three, be, and the same is hereby, so amended as to remove the limitation of the number of ordinary members of said Academy as provided in said act. Approved, July 14, 1870. DEPARTMENT OF STATE, June 10, 1882. True copies. SEVELLON A. BROWN, Chief Clerk. AN ACT to authorize the National Academy of Sciences to receive and hold trust funds for the promotion of science, and for other purposes. Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That the National Academy of Sciences, incorporated by the act of Congress approved March third, eighteen hundred and sixty-three, and its several supplements, be, and the same is hereby, authorized and empowered to receive bequests and donations, and hold the same in trust, to be applied by the said Acad. emy in aid of scientific investigations, and according to the will of the donors. Approved, June 20, 1884. DEPARTMENT OF STATE, June 24, 1884. A true copy. SEVELLON A. BROWN, Chief Clerk. REPORT OF THE NATIONAL ACADEMY OF SCIENCES. SESSIONS OF THE NATIONAL ACADEMY. During the year 1895 the Academy held four sessions. The first was a special session, held in New York, February 9. The second was the regular annual meeting, held at Washington, April 16 to 19. The third was a scientific session, held in Philadelphia, October 30 to November 1, and the fourth a special meeting, held at Philadelphia, October 31, for the transaction of business. SPECIAL MEETING. [New York, February 9, 1895.] This meeting was held at Columbia College, the president, Prof. O. C. Marsh, presiding. The following named members were present during the session: Marsh, Abbot, Barker, Billings, Brewer, Chandler (C. F.), Comstock, Gould, Hastings, Mayer, Mayo-Smith, Michelson, Rood, Rowland, Walker. No papers were read at this session, which was called for business only, namely, to comply with a law of Congress entitled "An act to define and establish the units of electrical measure," approved July 12, 1894, and announced to the Academy at the special meeting in New Haven, October 31, 1894. The president, Mr. Marsh, informed the Academy that on receiving a certified copy of the law from the Department of State he had appointed a special committee to investigate the subject. The act in question is as follows: AN ACT to define and establish the units of electrical measure. Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That from and after the passage of this Act the legal units of electrical measure in the United States shall be as follows: First. The unit of resistance shall be what is known as the international ohm, which is substantially equal to one thousand million units of resistance of the centimeter-gram-second 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 fourteen and four thousand five hundred and twenty-one ten-thousandths grams in mass, of a constant cross-sectional area, and of the length of one hundred and six and three-tenths centimeters. Second. The unit of current shall be what is known as the international ampere, which is one-tenth of the unit of current of the centimeter-gram-second system of electro-magnetic units, and is the practical equivalent of the unvarying current, which, when passed through a solution of nitrate of silver in water in accordance with standard specifications, deposits silver at the rate of one thousand one hundred and eighteen millionths of a gram per second. Third. The unit of electro-motive force shall be what is known as 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 an international ampere, and is practically equivalent to one thousand fourteen hundred and thirtyfourths of the electro-motive force between the poles or electrodes of the voltaic cell known as Clark's cell, at a temperature of fifteen degrees centigrade, and prepared in the manner described in the standard specifications. Fourth. The unit of quantity shall be what is known as the international coulomb, which is the quantity of electricity transferred by a current of one international ampere in one second. Fifth. The unit of capacity shall be what is known as the international farad, which is the capacity of a condenser charged to a potential of one international volt by one international coulomb of electricity. Sixth. The unit of work shall be the joule, which is equal to ten million units of work in the centimeter-gram-second system, and which is practically equivalent to the energy expended in one second by an international ampere in an international ohm. Seventh. The unit of power shall be the watt, which is equal to ten million units of power in the centimeter-gram-second system, and which is practically equivalent to the work done at the rate of one joule per second. Eighth. The unit of induction shall be 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. SEC. 2. That it shall be the duty of the National Academy of Sciences to prescribe and publish as soon as possible after the passage of this Act, such specifications of details as shall be necessary for the practical application of the definitions of the ampere and volt herein before given, and such specifications shall be the standard specifications herein mentioned. To meet this requirement of Congress it was necessary, in accordance with the constitution of the National Academy of Sciences, to appoint a special committee to consider the subject. This was done as soon as an official copy of the law was received from the State Department. The committee, selected from members of the National Academy, was as follows: Prof. H. A. Rowland, chairman, Johns Hopkins University, Baltimore. Prof. G. F. Barker, University of Pennsylvania, Philadelphia.. Prof. J. Trowbridge, Harvard University, Cambridge. Prof. C. S. Hastings, Yale University, New Haven. Dr. C. Barus, Smithsonian Institution, Washington. The committee completed the work assigned to them. The specifications they prepared meet the requirement of the law, and are also in accord with international agreement. These specifications are as follows: SPECIFICATIONS FOR THE PRACTICAL APPLICATION OF THE DEFINITIONS OF THE AMPERE AND VOLT. SPECIFICATION A.-The ampere. In employing the silver voltameter to measure currents of about 1 ampere, the following arrangements shall be adopted: The kathode on which the silver is to be deposited shall take the form of a platinum bowl not less than 10 centimeters in diameter and from 4 to 5 centimeters in depth. The anode shall be a disk or plate of pure silver some 30 square centimeters in area and 2 or 3 millimeters in thickness. This shall be supported horizontally in the liquid near the top of the solution by a silver rod riveted through its center. To prevent the disintegrated silver which is formed on the anode from falling upon the kathode, the anode shall be wrapped around with pure filter paper, secured at the back by suitable folding. The liquid shall 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. Method of making a measurement.-The platinum bowl is to be washed consecutively with nitric acid, distilled water, and absolute alcohol; it is then to be dried at 160° C., and left to cool in a desiccator. When thoroughly cool it is to be weighed carefully. It is to be nearly filled with the solution and connected to the rest of the circuit by being placed on a clean insulated copper support to which a binding screw is attached. The anode is then to be immersed in the solution so as to be well covered by it and supported in that position; the connections to the rest of the circuit are then to be made. Contact is to be made at the key, noting the time. The current is to be allowed to pass for not less than half an hour, and the time of breaking contact observed. The solution is now to be removed from the bowl and the deposit washed with distilled water and left to soak for at least six hours. It is then to be rinsed successively with distilled water and absolute alcohol and dried in a hot-air bath at a temperature of about 160° C. After cooling in a desiccator it is to be weighed again. The gain in mass gives the silver deposited. To find the time average of the current in amperes, this mass, expressed in grams, must be divided by the number of seconds during which the current has passed and by 0.001118. In determining the constant of an instrument by this method the current should be kept as nearly uniform as possible and the readings of the instrument observed at frequent intervals of time. These observations give a curve from which the reading corresponding to the mean current (time average of the current) can be found. The current, as calculated from the voltameter results, corresponds to this reading. The current used in this experiment must be obtained from a battery and not from a dynamo, especially when the instrument to be calibrated is an electrodynamometer. SPECIFICATION B.-The volt. Definition and properties of the cell.-The cell has for its positive electrode, mercury, and for its negative electrode, amalgamated zinc; the electrolyte consists of a saturated solution of zinc sulphate and mercurous sulphate. The electromotive force is 1.434 volts at 15° C., and, between 10° C. and 25° C., by the increase of 1° C. in temperature, the electromotive force decreases by .00115 of a volt. (1) Preparation of the mercury.-To secure purity it should be first treated with acid in the usual manner and subsequently distilled in vacuo. 2. Preparation of the zinc amalgam.-The zinc designated in commerce as "commercially pure" can be used without further preparation. For the preparation of the amalgam one part by weight of zinc is to be added to nine parts by weight of mercury, and both are to be heated in a porcelain dish at 100° C., with moderate stirring until the zinc has been fully dissolved in the mercury. 3. Preparation of the mercurous sulphate.-Take mercurous sulphate, purchased as pure, mix with it a small quantity of pure mercury, and wash the whole thoroughly with cold distilled water by agitation in a bottle; drain off the water and repeat the process at least twice. After the last washing, drain off as much of the water as possible. (For further details of purification, see Note A.) 4. Preparation of the zinc sulphate solution.-Prepare a neutral saturated solution of pure recrystallized zinc sulphate, free from iron, by mixing distilled water with nearly twice its weight of crystals of pure zinc sulphate and adding zinc oxide in the proportion of about 2 per cent by weight of the zinc sulphate crystals to neutralize any free acid. The crystals should be dissolved with the aid of gentle heat, but the temperature to which the solution is raised must not exceed 30° C. Mercurous sulphate, treated as described in 3, shall be added in the proportion of about 12 per cent by weight of the zinc sulphate crystals to neutralize the free zinc oxide remaining, and then the solution filtered, while still warm, into a stock bottle. Crystals should form as it cools. 5. Preparation of the mercurous sulphate and zinc sulphate paste.-For making the paste, two or three parts by weight of mercurous sulphate are to be added to one by weight of mercury. If the sulphate be dry, it is to be mixed with a paste consisting of zinc sulphate crystals and a concentrated zinc sulphate solution, so that the whole constitutes a |