John Addington Symonds (1840 - 1893) was an English poet and literary critic. Although he married and had a family, he was an early advocate of male love (homosexuality), which he believed could include pederastic as well as egalitarian relationships. He referred to it as l'amour de l'impossible (love of the impossible). A cultural historian, he was known for his work on the Renaissance, as well as numerous biographies about writers and artists. He also wrote much poetry inspired by his homosexual affairs. Read more on Wikipedia
Lowry quotes the lines of Symonds's opening section called 'The Choirster' from the long poem 'In Black and White - Winter Etchings' contained in the collection Vagabunduli Libellus 1884; "Snow on the high pitched minster roof and spire; snow on the boughs of leafless linden trees; snow on the silent streets and squares that freeze. Under night's wing, down drooping nigh and nigher." (Pg. 117) and "Inside the church within the shadowy choir dim burn the lamps like lights on vaporous seas. Drowsed are the voices of droned litanies. Blurred as in dreams the voice of priest and friar, Cold have numbed sense to slumber here!" (Pg. 117); and later; "Cold have numbed sense to slumber here! Then hark, one swift soprano, soaring like a lark, beats around arch and aisle, echoing dark with exquisite aspiration; throbs that soul of fire, higher, higher yearning with sharp anguish of untold desire." (Pg.118). Lowry slightly changes the wording of the last quote from the original poem. The poem is probably inspired by Symonds's love for Willie Dyer, a chorister at Bristol Cathedral.
Lowry must have been aware that 'The Choirster' was about a gay love affair as Symond's sexuality was well known. This raises some questions as to why he transposed the lines into Ultramarine as Dana struggles with his love for Janet Travena in Chapter 3.