estimate of the error involved in reading the graph. The Kubic harmonic expansion method using the parameters given by Betts 2 was applied in an attempt to obtain more accurate results. We calculated 0 0 to four different degrees of approximation by truncating the expansion at the third-, sixth-, ninth-, and fifteenthorder terms. The results were 166.54, 174.93, 176.82, and 176.71°K, respectively. The convergence appears to be satisfactory and the values after the first are in agreement with the result obtained using Leibfried's graph. The error involved in the calculation is probably negligible compared to the errors due to the uncertainties in the experimentally measured quantities used in the calculation. These latter errors contribute less than O.SoK using the errors quoted above and in the references. We, therefore, quote a value for 0 0 of 176. 7°±O.S°K. Previous measurements of 0 have been made by calorimetric means. Parkinson and Quarrington J4 have 14 D. H. Parkinson and J. E. Quarrington, Proc. Phys. Soc. (London) 67 A, 41 (1954). JOURNAL OF APPLIED PHYSICS measured the molar heat of PbTe and compute 0 for temperatures between 20 0 K and 160°K. They find values which range between 115°K and 140°K. Cochran et al.,15have made a calculation of 0 as a function of temperature using the frequency distribution of normal modes of vibration obtained from an inelastic neutron scattering experiment. Choosing a particular model, they present results for 0 which lie some 5% lower than the data of Parkinson and Quarrington. Extrapolating to OaK, they predict 0 to be about 166°K, about 5% lower than our value of 176.7°K. ACKNOWLEDGMENTSWe would like to express our appreciation to Frank Bis for his assistance in the crystal growth and to Elmer Gubner for his assistance in the density measurements.Thin films of MnBi possess many unusual physical properties and are particularly suitable for memory applications using laser Curie-point writing and magneto-optical readout. Films prepared on mica substrates have the easy direction of magnetization perpendicular to the film plane. They typically have a specific Faraday rotation of 5Xl()5 deg/cm, and an absorption coefficient of 3.8X1OS cm-1 for 6328 A wavelength, permitting a readout rate of 10 9 bits/sec at 1 mW laser power level using available detectors. Curie-point writing and erasing of a spot a few microns in diameter in a 1000 A thick film with a 4 j.tsec pulse from a 13 mW Gaussian laser beam have been achieved. For a 10 6 bits/cm 2 packing density, heating at adjacent spots is negligible. Calculations show that the writing magnetic field can be reduced to less than 10 Oe by using a memory plane consisting of discrete squares of MnBi. Analytical and experimental results as well as memory design considerations are presented.

High refractive index prisms have been used to couple optical beams into the thin film waveguides. To scan through various propagating modes normally requires rotating and repositioning of the prism-waveguide assembly. We have found that the required adjustment of the prism-position can be eliminated during the scanning of the various modes if the prism is properly offset with respect to the rotational axis. An analysis and a computer program are given for the calculation of this prism offset position on the basis of minimum deviation within the specified limits of the prism rotational angle.

Multimode optical channel waveguides are produced on filter glass wafers using a scanning focussed Ar laser beam. The localized refractive index change produced by the laser heating is measured and analyzed. The waveguide cross-sectional area is related to the laser power and scanning speed. Potential applications of this technique of channel waveguide fabrication are presented.

In this paper are studied the electron scrubbing and life tests for microchannel plates used in second generation image intensifiers. It presents the test apparatus developed specially for such tests and inquires into the proper schemes for the scrubbing process. Test results are analyzed and relevant conclusions drawn.

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