Once again documentary evidence shows that Joyce had no need for a neologism here. “Judas” has been used as an adjective (attributive noun) in English since the early fifteenth century, and the term “judas hand” was in metaphorical use in the nineteenth and early twentieth century, with writers relying on their readers’ familiarity with this passage from the Last Supper:
But, behold, the hand of him that betrayeth me is with me on the table. (Luke 22:21)
References to “Judas hand”, implying deceit, start to be recorded in the language from the 1820s. An early example from journalistic text occurs in the English Chronicle and Whitehall Evening Post of 1829, and suggests a political betrayal:
The Congress of Vienna protested against the Slave Trade. Portugal held out a Judas hand and received 300,000l to abolish it. How has she kept her faith? Why, during that last year she has shipped 50,000 negroes, 3,000 of whom died on the passage.
Twelve years later the metaphor is taken up again in Irish politics:
... while our sleeping Protestantism has been arr(!)oused to a sense of danger, and the defence of those liberties and institutions, which the Judas hand of Repeal would sell to our enemies for a “shout of the gulls " […]
The Repealer repulsed! A correct narrative of the rise and progress of the Repeal invasion of Ulster (1841, p.137)
The following quotation from Henry John Feasey’s Holy Week ceremonial of 1897 hints at a Christian ritual associated with the so-called “Judas candle” and sometimes with the Roman Catholic office of Tenebrae, “usually sung in the afternoon or evening of Wednesday, Thursday, and Friday in Holy Week, at which the candles lighted at the beginning of the service are extinguished one by one after each psalm, in memory of the darkness at the time of the crucifixion” (OED), where the fifteenth candle on the hearse is called the “Judas candle”:
At Albi it was not removed till the benediction of the font in the Vigil of Pentecost, and in some places it remained till after Pentecost — the flame being extinguished in holy water by means of a sponge, or by a (Judas) hand of wax.
This is confirmed by a passage from the Transactions of the Bristol and Gloucestershire Archaeological Society (1878, p. 93):
They were extinguished by a hand of wax, signifying the hand of Judas, of which our Lord said, “He who dippeth with me in the dish, &c.” In the old symbolism the wax meant flexible to evil.
The context of the piece of stage direction in the Circe episode that satirically uses elements from the library (Scylla and Charybdis) episode casts doubt on the religious interpretation proposed in Slote’s Annotations:
In John 8:12, Jesus says: ‘I am the light of the world: he that followeth me, walketh not in darkness, but shall have the light of life’; thus Judas would be that which strangles the light.
The scene refers to the gaslight in the brothel’s living room and Mananaun McLir’s slapstick impersonation of George Russell: “I am the light of the homestead!”. The dramatic interference of the skeleton Judas hand just requires a whore to adjust the mantle of the gas-jet to remedy the situation.