REPORT OF THE DIRECTOR OF THE BUREAU OF STANDARDS. DEPARTMENT OF COMMERCE AND LABOR, BUREAU OF STANDARDS, SIR: I have the honor to submit the following report of the work of the Bureau of Standards for the fiscal year ended June 30, 1909: DIVISION I.—ELECTRICITY. Electrical measuring instruments, of which a great variety of types and sizes are employed in the measurement of electrical current, voltage, and power, are tested by comparing them with certain standard instruments which have been carefully investigated and which are referred back from time to time to the fundamental electrical standards which it is one of the functions of the Bureau to establish and maintain. These fundamental electrical standards represent the unit of resistance and the unit of electromotive force or voltage, the values of which, and their method of preparation, are fixed by law. They are not, however, chosen arbitrarily, but are so specified as to be simply related to the absolute units of resistance and voltage, which latter are logically derived from the fundamental units of length, mass, and time-that is, the centimeter, the gram, and the second. The experimental realization of suitable concrete electrical standards involves two distinctly different steps or stages-first, the determination of their values by means of what are called "absolute electrical measurements," in which is demanded the complete theory of the methods and instruments employed, the most perfect instrumental equipment, and experimental skill of a high order; second, the development of concrete material standards by means of which the values found in these elaborate absolute measurements may be permanently preserved. This work was first done (chiefly by European investigators) a generation ago, and our present legal values were fixed on the recommendation of the International Electrical Congress of 1893. But subsequent work has shown that the values then adopted were not as accurate as they were supposed to be, and whereas England, France, America, and some other countries have continued to employ the values then chosen, Germany, Austria, and other countries have used slightly different units for the measurement of current and voltage. The International Electrical Conference which met in London in October, 1908, adopted a new value for the unit of electromotive force, but left to a newly constituted international committee the completion of the specifications of the concrete standards, inasmuch as agreement could not be reached at the conference. This committee of twenty members represents eleven different countries, three of the four American members, including the secretary and treasurer of the committee, being from the Bureau of Standards. In order to settle some of the disputed questions involved, and to clear up some of the obscure points at issue, the international committee has arranged to have an international cooperative investigation undertaken by representatives of some of the largest national standardizing institutions, including this Bureau; and at our invitation the work is to be carried out during the coming fiscal year at the Bureau of Standards. This work is of prime interest and importance, and will probably go far toward securing not only greater precision, but, what is even more important, international uniformity among the civilized nations of the world in electrical units and standards. In view of the international conference of last October and the approaching international cooperative investigation, considerable work has been done during the year on the subject of electrical standards and absolute electrical measurements. RESISTANCE AND ELECTROMOTIVE FORCE. Although the London International Electrical Congress selected the ohm and the ampere as the fundamental electrical units in terms of which all electrical measurements are to be expressed, the Bureau has found it impracticable to adopt the recommendations, owing to variations still found in coulometer measurements, which are at present under investigation. The results of electrical measurements will therefore be referred to the basis of reference heretofore employed, namely, the ohm and the Weston standard cell. During the past year considerable progress has been made in the construction of primary mercurial resistance standards. The calibration of a number of carefully selected capillary tubes has been completed, and considerable preliminary work has been done in other directions. Further work has been done in cooperation with the Chemical Division in the investigation of equilibrium conditions in the Weston normal cell, which have been called into question, and some promising results have already been obtained. The comparison of standard cells, set up during the past year, at the English National Physical Laboratory and by other investigators has verified the accuracy of reproduction claimed in former reports several parts in 100,000. An investigation of the conductivity and temperature coefficient of copper and aluminum had been undertaken at the request of the committee on standards of the American Institution of Electrical Engineers and of a number of copper refiners and wire manufacturers who have generously offered to cooperate with the Bureau in furnishing and drawing samples. This work will include an investigation of commercial and specially prepared materials, the influence of traces of added impurities which so largely affect the conductivity, and the influence of drawing and annealing. An experimental and theoretical study has also been made of the vibration galvanometer used in precision measurements with alternating currents and has resulted in improvements which further increase its already high sensibility. The above investigations will be continued as far as permitted by the routine testing of apparatus submitted for certification, the volume of which has shown a steady increase since the organization of the Bureau. INDUCTANCE AND CAPACITY AND ABSOLUTE MEASUREMENTS. The work on the absolute measurement of electric current has been continued during the year and a new value obtained for the electromotive force of the Weston normal cell. An investigation of the silver coulometer is being carried out, which promises to yield results of much scientific value. A new method for the absolute measurement of resistance has been devised, and the necessary apparatus constructed; work of carrying out the measurements will be done during the next fiscal year. Investigations of inductances and condensers have been continued. Tests have also been made of standards of inductance and capacity and of electrical instruments. The work in this section touches the practical application of electricity less directly than in other sections of the Electrical Division, being largely concerned with the fundamental measurements which underlie practical applications. MAGNETIC MEASUREMENTS. The principal demands for magnetic testing comprise tests to determine the magnetic permeability of specimens and to determine the energy losses occurring in the magnetic material used in the construction of electrical apparatus, such as dynamos, motors, and transformers. Improved methods for conducting both of these tests have been in the course of development for some time, and have now reached a satisfactory stage. Circular No. 17 has been issued, announcing the readiness of the Bureau to conduct magnetic tests for the public and prescribing the conditions under which tests are made. The Bureau has prepared a number of bars of different grades of steel, and different sizes, whose magnetic properties have been carefully determined. These are supplied to the public, when desired, for the purpose of checking magnetic measurements made with commercial or other apparatus. Preparations have been made for testing the spirals of bismuth wire which are used for the measurements of intense magnetic fields, and several of these spirals have been tested. Special investigations were completed during the year to determine the effects of high temperatures and of low temperatures upon the magnetic properties of manganese-steel, the alloy used being one which is very nearly nonmagnetic; to determine the errors incident to testing material in the form of rings; to discover whether the energy losses due to alternating magnetization are dependent upon the wave form of the electrical current used for magnetizing, and to determine the relative merits of silicon-steel and ordinary steel for use in electrical transformers. |