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 amplifier1 and with a cathode ray oscillograph and a capacity-coupled amplifier,2 but 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 Toennies3 and by Adrian and Matthews,4 but we