The paper describes in detail how the testing of current transformers may be carried out with speed and accuracy by means of a potential-divider bridge. The corrections to be made to the readings are deduced from the theory of the bridge; and it is shown that, by taking a few simple precautions, an accuracy of 0.01 per cent for ration measurements, and of 0.1 minute for phase-angle measurements, is attainable if the transformer characteristics are stable to this limit.A very sensitive and accurate bridge, which is not so convenient for general purposes as the potential-divider bridge, is than described. Results obtained with this bridge are compared with those obtained with the potential-divider bridge, and found to be in close agreement.