The Hall Effect in bismuth for a magnetic field strength of from 0.07 to 1.00 gauss was accurately determined by improved methods. Production of the bismuth films. Various methods for obtaining excessively thin, homogeneous bismuth films were tried and compared, such as casting, electroplating, evaporating, sputtering, and metallic spraying, of which the last three methods were particularly successful. Measurement of very low voltages. By refinements made in the potentiometer and measuring circuits readings to one-tenth microvolt were accurate and reproducible. Magnitude of the Hall Effect at low fields. A curve is plotted showing the rapid decrease in the value of -R between 0.07 and 0.30 gauss, and comparison is made with the higher values of field strength. It is noted that by putting the Hall potential of one film in series with one or more other films we obtain comparatively high values of the Hall e. m. f. which may be applied to great advantage as an alternating current rectifier in radio and similar applications.