"To account for the idea of time, it appears to me to be sufficient to attend to a few well known facts, viz. that impressions made by external objects remain a certain space of time in the mind, that this time is different according to the strength, and other circumstances of the impression, and that traces of these impressions, i. e. ideas, may be recalled after the intervention of other trains of ideas, and at very different intervals."
— 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>