"Are not these as plain proofs, that the passions of fear and hope are mixtures of grief and joy, as in optics it is a proof, that a coloured ray of the sun passing through a prism, is a composition of two others, when, as you diminish or encrease the quantity of either, you find it prevail proportionably more or less in the composition?"
— Hume, David (1711-1776)
David Hume, A Treatise of Human Nature. Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects. 3 vols. (London: Printed for John Noon, 1739; Thomas Longman, 1740). <Link to ESTC><Link to ECCO><Link to ECCO-TCP><Link to OLL>
Reading David Hume, A Treatise of Human Nature, eds. D. F. and M. J. Norton (Oxford: OUP, 2000). Searching in Past Masters and OLL editions.