An instrument for exhibiting optically or graphically these variations is called an oscillograph, or sometimes an ondograph.
Hospitalier are examples; (3) methods employing a high-frequency galvanometer or oscillograph, which originated with A.
Blondel, and are exemplified by his oscillograph and that of W.
In the Duddell oscillograph it is usual to place a pair of loops in the magnetic field, each with its own mirror, so that a pair of curves can be delineated at the same time, and if there is any difference in phase between them, it will be detected.
In one form of Blondel's oscillograph, the vibrating system is a small magnetic needle carrying a mirror, but the principle on which it operates is the same as that of the instrument above described.
The oscillograph can be made to exhibit optically the form of the current curve in non-cyclical phenomena, such as the discharge of a condenser.
A form of thermal oscillograph has been devised by J.
See Assoc. Franc. pour l'Avanc. des Sciences (1898), for a paper on oscillographs describing Blondel's original invention of the oscillograph in 1891.
(London, 1901), which contains a list of original papers on the oscillograph; Id., The Principles of Electric Wave Telegraphy (London, 1906), which gives illustrations of the use of the oscillograph and the Braun cathode ray tube in depicting condenser discharges; also, for the development of the oscillograph, A.