A mystical element runs through Stephen's meditations on the "Ineluctable modality of the visible." Thinking "Signatures of all things I am here to read," he recalls the De Signatura Rerum ("On the Signatures of Things"), published in 1622 by a Lutheran theologian named Jakob Böhme (usually written Boehme in English).
Boehme had a number of mystical experiences as a young man, including one in 1600 in which the sight of a sunbeam reflected in a metal dish revealed to him the spiritual beauty of the universe. Further visions included one in which he walked out into the fields and saw there signs of the divine creator visibly manifested in all created things. Stephen aspires to "read" such divine signatures in the sights he encounters on the seashore: "seaspawn and seawrack, the nearing tide, that rusty boot. Snotgreen, bluesilver, rust: coloured signs."
The mystical burden of the Signatura appears in Stephen's thoughts in the next paragraph, as he closes his eyes and turns his attention to "the ineluctable modality of the audible": "Am I walking into eternity along Sandymount strand?" The answer, unfortunately, is No. When he opens his eyes two paragraphs later the created world has not "vanished," and he is not "for ever in the black adiaphane".
The Signatura argues that direct apprehensions of divine truth are a necessary complement to mere faith. Gifford quotes from the beginning of the work: "All whatever is spoken, written or taught of God, without the knowledge of the signature is dumb and void of understanding; for it proceeds only from an historical conjecture, from the mouth of another, wherein the spirit without knowledge is dumb; but if the spirit opens to him the signature, then he understands the speech of another; and further, he understands how the spirit has manifested and revealed itself . . ."
This argument falls within a long Christian tradition of regarding the Book of Nature as a second source of divine revelation, complementary to the Book of Scripture. But a thread of Neoplatonism runs through Boehme's writings and, like many mystics, he took some doctrinal positions that violated orthodox theological teaching, arousing opposition from Lutheran authorities.
In an endnote to his biography, Ellmann reproduces the surviving part of an inventory that Joyce made of his books before leaving Trieste (785-87). On the list is "Jacob Behmen, The Signature of All Things." Apparently Joyce read the work in this 17th century English translation by John Sparrow, from which Gifford quotes.