"Parallax" is an optical phenomenon that lets astronomers mathematically compute the distances to nearby stars, but the basic idea is not technical, otherworldly, or difficult to grasp. In Lestrygonians Bloom thinks of it as a something that "I never exactly understood," but he recalls what Molly has said about another such word, metempsychosis: "She's right after all. Only big words for ordinary things on account of the sound." The Greek word means simply "alteration" (parallax is the adverbial form) and scientists use it for the way the position of an object appears to change when the position of the observer changes. Joyce goes out of his way to suggest that Bloom could, should, and even perhaps latently does understand this meaning. Metaphorically, it is characteristic of his thought processes and of the narrative art of Ulysses.

JH 2021

Undated copy, probably early 1900s, of Sir Robert Ball's The Story of the Heavens (first published 1886). Source:

Dublin's Dunsink Observatory, photographed by David Malone in 2002. Source: Wikimedia Commons.

The parallax angle (p) used to calculate distance (d). Source:

Parallax as demonstrated by closing first one eye and then the other. Source:

Illustration of two kinds of binocular vision in mammals, showing the rabbit's small sliver of stereoscopic depth perception and the monkey's larger one. Source:

Parallax as demonstrated by looking at a star in January and July. Source:

Degrees of difference in parallax angles seen in relation to different distances. Source:

Parallax as demonstrated by looking out the window of an automobile from two different points on the road. Source: