Engraving and printing methods, advertisement illustration, technical- and trade-paper advertising, street-car advertising, outdoor advertising, house publications (1909)
Scranton : International Textbook Co. · leaf 293
Fig. 54 Fig. 55 Fig. 58, where the spot a is twice the size of spot b, but itslight-and-shade value is only half as strong as b, and thereforethese two are balanced when equidistant from the center c,
