A Precision Determination ofheby Means of the Short Wave-Length Limit of the Continuous X-Ray Spectrum at 20 kv

A redetermination of $\frac{h}{e}$ by the method of the short wave-length limit of the continuous x-ray spectrum was undertaken in order to obtain further evidence as to the discrepancy among the determinations of atomic constants. The accuracy of the experiment is improved by (1) large primary x-ray intensity, (2) the use of a high resolving power double crystal spectrometer, (3) reduction in background and improvement in the sharpness of the limit by the use of balanced filters, (4) improved accuracy in voltage measurements, and (5) cleaning the target in vacuum. The sources of error both in the measurements and the interpretation of the data are discussed. Our result is $\frac{h}{e}=(1.3786\mathrm{}\pm 0.0002)\times {10}^{-17\mathrm{}}$ erg sec./e.s.u. This value is found to be in fair, though not complete, agreement with measurements of other atomic constants.