[en] 24,850. Fleming, J. A. Nov. 16. Vacuum tubes. - Alternating currents of high frequency, particularly those employed in wireless telegraphy, are rectified by means of an apparatus consisting of a highly-incandescent conductor and a cold conductor enclosed in a highly-exhausted vessel. Negative electricity can pass from the hot conductor, but not to it, through the vacuum. The incandescent conductor is preferably a carbon filament b heated by a current from an insulated battery h, and should be heated to nearly 1700 C. The cold conductor is preferably platinum, aluminium, or carbon, and may be in the form of a tube c surrounding the filament.