In the present report an efficient and flexible method for recording tremor is described. Numerous ways of obtaining graphs with a Marey tambour, or related apparatus, have been devised, of which that used by de Jong1 is one of the most recent and best.
The method reported here utilizes a rubber diaphragm over the rim of an ordinary "balanced armature" loud speaker. The cone has been sealed with multiple layers of collodion and the rubber diaphragm cemented with rubber cement to assure air tightness within the chamber. With the tremulous hand placed on the diaphragm, motion is transmitted mechanically and produces variation in the reluctance of the magnetic path, which thus sets up in the alternating current coils a varying electromotive force. This, in turn, is amplified and recorded by the electromagnetically operated ink-writing pens of a Grass electroencephalograph.2 The paper can be run at different speeds, 3 cm.
Morris AA. AN APPARATUS TO BE USED IN RECORDING TREMORS. Arch NeurPsych. 1943;49(1):123-125. doi:10.1001/archneurpsyc.1943.02290130131014