Records of magnetic field as a function of altitude have been obtained from total‐field magnetometers mounted in two Aerobee sounding rockets which were fired from the seaplane tender USS Norton Sound in March 1949. The flights were made 60 miles apart at approximately 89° west longitude, 11° south latitude, or geomagnetic longitude 341°, geomagnetic latitude −1°. The first rocket, Aerobee Round A‐10, was fired on March 17 at 17h 20m 90th meridian time; Round A‐11 was fired on March 22 at 11h 20m 90th meridian time. In Aerobee A‐10 the field decreased between 20 and 105 km in accordance with the simple dipole field, while in Aerobee A‐11 a discontinuity of 4±0.5 milligauss was observed in the altitude range of 93 to 105 km. These results (1) establish experimentally the existence of a current system in the E‐region of the ionosphere which is responsible for the diurnal variation of the earth's magnetic field at sea level; and (2) lend strong support to the dynamo theory of the daily magnetic variation which was originally proposed by Balfour Stewart and Schuster.

An Aerobee rocket containing a total‐field magnetometer was fired, and telemetered data gave a record of the earth's magnetic field during the flight. The recorded decrease in field was 28 milligauss (mG) at 368,000 feet, which agreed with dipole calculations to within 2 mG. This was the first step in an attempt to obtain direct experimental evidence of postulated current‐sheets in the upper atmosphere. The flight was intended chiefly as a test of the method and instrumentation, and was made at White Sands because of existing facilities there. The location was unfavorable to the ultimate purpose of the experiment, and no evidence of magnetic fields caused by current‐sheets was obtained. The results show, however, that the method is adequate for detection of the predicted effects at more favorable geomagnetic latitudes.

The 4-hour period was assigned to La 133 by the mass spectrograph method. Figure 1 shows the original photographic plate PUBLICATION of brief reports of important discoveries in J-physics may be secured by addressing them to this department. The closing date for this department is five weeks prior to the date of issue. No proof will be sent to the authors. The Board of Editors does not hold itself responsible for the opinions expressed by the correspondents. Communications should not exceed 600 words in length. i i gd^^mp^^gggp^g H mmi0 . Ti

LETTERS TO THE EDITOR 957 indicated on the graphs. Measurements were made at 4600, 4900, 5200, and 5500 Mc/sec in a guide with cutoff at 4430 Mc/sec, over a range of gas pressures from 0.5 to 100 mm Hg, and at various dc pulse currents and voltages.The results obtained are readily explained in terms of decomposition of the "linear" TEn wave into two oppositely-rotating circularly-polarized waves, an "anomalous" and a "normal" wave. The "anomalous" wave exhibits, in the region of gyromagnetic resonance, very strong attenuation and a reversal of the sign of its phase shift with respect to propagation in vacuum. The "normal" wave is only slightly attenuated in this region and accounts for the circular polarization observed at gyromagnetic resonance.The roles of "anomalous" and "normal" waves are interchanged if the sense of the magnetic field is reversed. Consequently, each of the circularly-polarized waves is heavily attenuated by one or the other of two opposing magnetic fields, both at gyromagnetic resonance. This fact enabled the construction, with two independent solenoids, of a microwave analogue of crossed Nicol prisms.The circularly-polarized waves are not true propagating modes through the plasma in these experiments. Our interpretation remains, however, valid because a short section of plasma was employed. The theoretical details have been worked out for the case of the unbounded anisotropic plasma, including electron collision effects. Further theoretical work remains for the wave guide case.These results hold promise as a tool for the study of gas discharge phenomena. They are applicable also to switching, amplitude, phase or frequency modulation, and polarization control in an electronically controllable medium.

No abstract