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, 1911: The work of the Bureau has shown steady progress in its various divisions. The number of tests increased to considerably more than double that of the previous year. This growth is due to the steadily increasing interest of the industries in applying scientific data and principles to manufacturing. The great demand for investigations and information has taxed the available force to meet it. A noteworthy feature of the year's progress has been in the investigation and testing of structural materials. The completion of extended investigations affecting the fundamental electrical units and standards is also of special interest. ELECTRICITY. On the 1st of January, 1911, the Bureau adopted the new value for the international volt in accordance with the recommendation of the International Committee on Electrical Units and Standards. This unit was adopted at the same time in England, France, Germany, and many other countries, thus securing, for the first time, close international agreement in the measurement of electrical voltage and current. This agreement was reached as a result of the cooperative investigation which was made at the Bureau of Standards by representatives of several national standardizing laboratories, an account of which was given in my report of one year ago. The investigations carried on during this period of cooperation have been continued with a view of further perfecting the official specification of standard cells and the silver voltameter. ELECTRICAL STANDARDS. The investigation on the absolute measurement of current, which is of great importance in connection with electrical standards, has been completed and the results prepared for publication. The object of this research has been not simply to obtain a more accurate value of standard cells in terms of resistance standards and the absolute ampere, but also to develop and perfect the form of ampere balance employed. The construction of four primary mercurial resistance standards, in accordance with the specifications adopted by the London Inter national Electrical Conference of 1908, has been practically completed. The data from which the resistance assigned to the four standards are calculated were all determined to a high degree of precision, and the measured differences of the four tubes agree with the calculated differences to within 5 parts per million, indicating the possibilities when the same procedure is followed throughout. The differences between the Bureau standards and those previously constructed in other national laboratories are somewhat greater, as might be expected. Two of these laboratories are undertaking the construction of new standards in accordance with the more rigorous London specifications here employed. The comparison of the new tubes with the Bureau tubes will furnish a better basis for estimating the accuracy attainable in the reproduction of the international ohm. PRECISION RESISTANCE MEASUREMENTS. This work includes the investigation of methods of resistance measurements, the design and investigation of resistance standards, the determination of the various electrical properties of conductors and the testing of resistance standards, bridges, precision rheostats, potentiometers, etc. During the past year there has been an increase in the number of resistance standards and other apparatus tested. Apparatus for the accurate establishment of a resistance ratio of 10 to 1 has been constructed according to the Bureau specifications and now replaces the apparatus formerly used in "building up." A few resistance standards have been constructed, using a new alloy. While these have been under observation only a few months, the indications are that the new alloy will be found to be as good or better than manganin for use in resistance standards and resistance apparatus. A study has been made both of resistance standards having four terminals and of the Thomson bridge. The results of this investigation are to be published in the Bulletin of the Bureau. ELECTRICAL MEASURING INSTRUMENTS. During the year an extended investigation of direct current switchboard instruments was completed and the results prepared for publication in order to make the detailed data available to manufacturers and users of instruments. An electrodynamometer capable of carrying currents up to 5,000 amperes has been designed and constructed. A careful study of current transformers and of the methods used in determining their constants has been carried out. The results of this investigation are being published, as are also descriptions of some new types of potentiometers especially designed for the rapid and accurate testing of electrical measuring instruments and for the accurate measurements necessary in electrical engineering. A device for measuring the torque of instruments was designed and constructed and a description of it published. During the year a relatively large number of tests requiring the measurement of torque were made. A standard variable self and mutual inductance was constructed for use in general testing work. Several other investigations have been |