First mentioned in 16th century literature, magic lanterns such as this one were very popular in the late 19th century, and were used to project images of famous landmarks, foreign lands and famous people. By the early 20th century when Nabokov was growing up, however, the moving picture was rapidly replacing this early slide projector, and perhaps Nabokov is disdainful of the machine because it reminded him of the archaic past. Or perhaps he found magic lantern projections to be a 'philistine' or bourgeois occupation. (see Nabokov's Lecture "On Philistines and Philistinism")
It may be worth mentioning that magic lanterns featured heavily in Marcel Proust's childhood, as described in A la Recherche du Temps Perdu. Is Nabokov trying once again (see bookmark to page 75) to hitch his childhood to the French literary giant's? Or is he once again playing with the reader's knowledge of literary classics?