Interest in the study of surge-voltage distribution in transformers has been stimulated by the increasing attention given to the impulse strength of transformers. Experimental methods of investigating surge phenomena necessitate the use of the cathode-ray oscillograph, and for transformer work the recurrent-surge oscillograph method has important advantages. As low voltages are used there is no risk of damage to the transformer. The recurring trace is peculiarly suitable for visual observation and eliminates most of the difficulties associated with single transient recording.This paper assesses the value of the recurrent-surge oscillograph for transformer investigations and deals briefly with its development and design. A description is given of the latest E.R.A. instrument, which incorporates some special features.Methods of applying the recurrent-surge oscillograph to transformers are discussed, and its position with regard to transformer research is reviewed principally with reference to the work of the Electrical Research Association.