In previous articles8 it was shown that difficulties inherent in the commutator rendered the commutator-potentiometer system undesirable for the measurement of overvoltage and transfer resistance. The present article is a description of a commutator oscillograph system which is much superior for such determinations.The moving coil oscillograph has been used by Reichinstein,4 *LeBlane,6 Lattery6 and Miller7 in studies of transient phenomena at electrode surfaces in electrolytes. In all these cases a source of intermittent direct current was used and the electrodes were connected directly to the oscillograph. The method was finally rejected because the oscillograph drew considerable current for its operation and thus changed the potentials of the electrodes under investigation while those potentials were being measured. This difficulty was partially overcome by Holler8 through the use of a vacuum tube amplifier. He used the new arrangement to study polarization and the nature of "transfer resistance" or as he called it "boundary resistance." His oscillograph required 150 milliamperes for full-scale deflection which made it necessary to use a three-tube amplifier. Even then it required 15 millivolts change in grid potential to produce a change of 1 milliampere through the oscillograph circuit; which means the arrangement is not suitable for accurate work.The cathode ray oscillograph has been adopted by Newbery9 for the study of polarisation and overvoltage. It is ideal in respect to its capacity to accurately follow extremely rapid changes of potential. Vibrations having a frequency of 106 per second may be recorded. It is also especially desirable in that it draws practically no current from the source. A marked disadvantage, however, is that it gives a deflection of only one millimeter per volt. By the use of an amplifier it is possible to secure deflection of one millimeter per 100 millivolts. Another very serious difficulty is that the