Alternating.

Principles of alternating currents Lawrence, Ralph, Restieaux 1922 Symmetrical component analysis of unsymmetrical poly-phase systems Neumann, Reginald. [from old catalog] 1939 The measurement of alternating current energy Canfield, D. T. 1940 The rectification of alternating current Rissik, Hendrik 1938 Theory & calculation of alternating currents Lee, Bernard Crossley. [from old catalog] 1948 Theory and practice of alternating currents Dover, Alfred Thomas 1947 Theory and practice of alternating currents Dover, A. T. 1947