"To assist the imagination, indeed, but by no means in any consistency with the notion of a nervous fluid, it had been conceived that ideas resembled characters drawn upon a tablet; and the language in which we generally speak of ideas, and their affections, is borrowed from this hypothesis."
— Priestley, Joseph (1733-1804)
See Hartley’s Theory of the Human Mind, on the Principle of the Association of Ideas; With Essays Relating to the Subject of It. By Joseph Priestley, LL. D. F. R. S. (London: Printed for J. Johnson, No. 72, St. Paul’s Church-Yard, 1775). <Link to ESTC>