High lights

D-C Transformers. Various methods have been proposed for transforming voltage on d-c systems without using a motor-generator set. Although little practical use has been made of the device, the d-c transformer using grid-controlled mercury-arc rectifiers for commutating the direct current is one of the more promising of the^¶ systems thus far devised. The general theory of d-c transformers is discussed in a paper in this issue, and 2 new types of d-c transformers using grid-controlled mercury-arc rectifiers are described (pages 1372–8).