Recent improvements in A-C. indicating instruments

C. G. Brown: As a-c. ammeters were previously made, the d-c. readings were so different according to the direction of flow of current that it was not feasible to calibrate on d-c. The metal in the moving system of the a-c. ammeter which Mr. Hoare has described has its direct and reversed d-c. readings so nearly alike that when necessary it can be checked on d-c.