“Still falls the Rain —
Dark as the world of man, black as our loss —
Blind as the nineteen hundred and forty nails
Upon the Cross.”

Source: Revolution

This is attributed, with an expression of doubt as to its correctness, in Mathematics, Our Great Heritage: Essays on the Nature and Cultural Significance of Mathematics (1948) by William Leonard Schaaf, p. 163; also attributed in Pi in the Sky : Counting, Thinking and Being (1992) by John D. Barrow. There are a number of similar expressions to this with various attributions, but the earliest published variants seem to be quotations of Lord Bowen:
When I hear of an 'equity' in a case like this, I am reminded of a blind man in a dark room — looking for a black hat — which isn't there.
Lord Bowen, as quoted in "Pie Powder", Being Dust from the Law Courts, Collected and Recollected on the Western Circuit, by a Circuit Tramp (1911) by John Alderson Foote; this seems to be the earliest account of any similar expression. It is mentioned by the author that this expression has become misquoted as a "black cat" rather than "black hat."
An earlier example with "hat" as a learned judge is said to have defined the metaphysician, namely, as a blind man looking for a black hat in a dark room, the hat in question not being there Edinburgh Medical Journal, Volume 3 (1898)
With his obscure and uncertain speculations as to the intimate nature and causes of things, the philosopher is likened to a 'blind man in a dark room looking for a black cat that is not there.'
William James, himself apparently quoting someone else's expression, in Some Problems of Philosophy : A Beginning of an Introduction to Philosophy (1911) Ch. 1 : Philosophy and its Critics
A blind man in a dark room seeking for a black cat — which is not there.
A definition of metaphysics attributed to Lord Bowen, as quoted in Science from an Easy Chair (1913) by Edwin Ray Lankester, p. 99
A blind man in a dark room looking for a black cat which isn't there.
A definition of metaphysics attributed to Lord Balfour, as quoted in God in Our Work: Religious Addresses (1949) by Richard Stafford Cripps, p. 72
A philosopher is a blind man in a dark room looking for a black cat that isn't there. A theologian is the man who finds it.
H. L. Mencken, as quoted in Peter's Quotations : Ideas for Our Time (1977) by Laurence J. Peter, p. 427
A metaphysician is like a blind man in a dark room, looking for a black cat — which isn't there.
Variant published in Smiles and Chuckles (1952) by B. Hagspiel
Misattributed

Still Falls the Rain (1940)

Source: South of the Border, West of the Sun

Pt. V, ch. 1, sec. 1.
1920s, Process and Reality: An Essay in Cosmology (1929)
Context: There is a greatness in the lives of those who build up religious systems, a greatness in action, in idea and in self-subordination, embodied in instance after instance through centuries of growth. There is a greatness in the rebels who destroy such systems: they are the Titans who storm heaven, armed with passionate sincerity. It may be that the revolt is the mere assertion by youth of its right to its proper brilliance, to that final good of immediate joy. Philosophy may not neglect the multifariousness of the world — the fairies dance, and Christ is nailed to the cross.

Source: Let the Great World Spin