The alternating current supply is a convenient source of current in frequency measurements and comparisons, unless high degree of constancy is desired. An ac arc also is.a fairly satisfactory intermittent source of light. A number of experiments are described, making useof these facts:
(1) The motion of a tuning fork and explanation of beats.
(2) Waves on liquids can be shown, including the case of beats.
(3) Slight phase changes may be shown when a heavy motor is connected to the line.
(4) An audio-oscillator may be calibrated.
(5) Reaction of closely and loosely coupled circuits may be mechanically demonstrated; and an explanation found for the difficulties sometimes encountered in Melde’s Experiment. Also, there are explained two useful theorems in connection with Lissajou figures.
PAUL F. GAEHR, "SOME USES OF ALTERNATING CURRENT SUPPLY," J. Opt. Soc. Am. 18, 488-488 (1929)