The Blackening of Photographic Emulsions by Low Speed Electrons

New type of electron spectrograph.—Electrons from an oxide coated filament are accelerated to a cylindrical anode, coaxial with the filament, having a narrow slit for one of its elements. The whole system is placed in a uniform magnetic field parallel to the filament. Those electrons which pass through the slit focus in the plane normal to that containing the filament and the slit. 22 volt electrons have been focused sharply. An extremely accurate direct determination of $\frac{e}{m}$ should be possible with this arrangement.