This article is from Newnes' 'Complete Electrical Engineering', Vol.3 I estimate it to be from the 1940s or 1950s

Thanks to Chris Colebrook for sending this article from  "The Practical Electrical Engineer" April 1933.

This page, describing a grid-controlled MAR is from "Power Wiring Diagrams" (A.T.Dover) 3rd edition 1936 (Reprinted 1952)