The HOME SECRETARY and the FOREIGN SECRETARY of the ACADEMY The CHAIRMAN and the PERMANENT SECRETARY of the NATIONAL RESEARCH COUNCIL WILLIAM DUANE, '23 A. L. DAY, '22 GANO DUNN, '22 J. M. CLARKE, '21 V. C. VAUGHAN INFORMATION TO SUBSCRIBERS SUBSCRIPTIONS TO THE PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES at the rate of $5.00 per annum should be made payable to the National Academy of Sciences, and sent either to Easton, Pa., or to C. G. ABBOT, Home Secretary, National Academy of Sciences, Smithsonian Institution, Washington, D. C. Single numbers, $0.50. PAST publications of the NATIONAL ACADEMY OF SCIENCES are listed in these PROCEEDINGS, Volume III, pp. 743-753, December, 1917. In good part these publications are no longer available for distribution. Inquiries with regard to them should be addressed to the Home Secretary, National Academy of Sciences, Smithsonian Institution, Washington, D. C. PAST volumes of the PROCEEDINGS may be obtained at five dollars per volume unless the sale of the volume would break a complete set of Volumes I to V. Single numbers may be obtained for fifty cents except where the sale of such numbers would break up a complete volume. Only two hundred complete sets of the Proceedings are available for sale-Volumes I to VI, price $30.00. Orders should be sent to the Home Secretary, National Academy of Sciences, Smithsonian Institution, Washington, D. C. The following publications are issued by the NATIONAL RESEARCH COUNCIL. Orders and inquiries should be addressed: Publication Office, National Research Council, 1701 Massachusetts, Ave., Washington, D. C. (A) THE BULLETIN OF THE NATIONAL RESEARCH COUNCIL published at irregular intervals; Price $5.00 per volume of about 500 pages; individual numbers priced variously. (B) THE REPRINT AND CIRCULAR SERIES OF THE NATIONAL Research COUNCIL, individual numbers, variously priced. Communicated by R. A. Millikan, Aug. 17, 1921 In a recent paper1 it was shown that the electrons could presumably travel through N2 and H2 gases in a free state at atmospheric pressure. It was found in some cases impossible to evaluate the mobilities of these electrons with the low frequencies of commutation available. The values of the mobilities indicated by these results appeared to be so much higher than the values obtained by earlier investigators that it was felt worth while to attempt to measure them accurately. The mobilities of electrons were accordingly determined in N2 using the high frequency oscillations obtained from two Western Electric Company "E" tube oscillators operating in parallel. The diagram of connections is shown in figure 1. In some cases the oscillations were taken directly from the primary condenser C1, and at other times from the condenser C2 of a secondary circuit tuned to resonance with the primary circuit. The method of measurement was the well known Rutherford alternating current method. The electrons used where photo electrons liberated by ultraviolet light from one of the plates. The ionization chamber used was similar to the one used in measurements of the constant of attachment of electrons to gas molecules, except that still greater precautions were taken in this chamber to avoid contamination. The measurements were made in the same manner as were the measurements for the determination of the coefficient of attachment. The current to the electrometer plate was measured as a function of the value of the alternating potential between the plates. This current was then plotted against the potential difference thus yielding a mobility curve. The potential difference Vo, at which this curve cut the axis was substituted in the equation, in order to evaluate the mobility U. In this equation n is the frequency of the alternations, d is the distance between the plates in cm. and Vo is the voltage in volts as read from the static voltmeter. In the oscillating circuits the potential was varied by varying the resistance r of the plate circuit. Since varying r altered the frequency n slightly the frequency of the oscillations was determined by means of a wave meter for several values of the voltage used in each determination. The experiments reported here covered a range of pressures from 600 mm. to 75 mm. The frequencies used varied from 7000 cycles per second to 150,000 cycles. The voltages used were varied from 10 volts to 300 volts and the plate distances lay between 2.0 cm. and 1.5 cm. The values of U thus obtained were reduced to give the mobility constant K at atmospheric |