Page:Collected Physical Papers.djvu/386

366 10, 20, or 200 vibrations per second. The writer is suspended at the centre of a circular electromagnet, the current in which is periodically interrupted by the reed C (fig. 116). When the writer and the reed are exactly tuned then the vibration of the reed throws the writer into a sympathetic vibration.

The reliability and accuracy of this method of automatic record of extremely short intervals of time is