North Side of the Altar
(The). The side on which the Gospel is read. The north is the dark part of the earth, and the Gospel is the light of the world which shineth in darkness- “illuminare his qui in tenebris et in umbrâ mortis sedent.” Facing the altar from the body of the church, the north side is on your left.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894