An Ink-Writing Electro-Encephalograph

The electrical potentials generated in the cerebral cortex may ultimately have considerable clinical as well as physiologic significance. Preliminary observations on these phenomena were carried out with a string galvanometer and a direct current amplifier1and with a cathode ray oscillograph and a capacity-coupled amplifier,2but it was soon evident that the most significant electrical waves had frequencies below 30 cycles per second and might therefore be successfully recorded by means of an ink-writing oscillograph. The advantages of obtaining an immediate permanent record on a paper tape at a cost of 1 cent per hundred feet are obvious. The problem was to obtain an ink-writing oscillograph with as high a frequency range as possible and to construct an amplifier to deliver to it sufficient current for its operation. Ink-writing oscillographs for this purpose have already been developed by Toennies3and by Adrian and Matthews,4but we