Plate, 'Instrument for making definite mixtures of the colours of the spectrum' by James Clerk Maxwell Early drafts of figures 1-2 showing different views of the construction of an apparatus used by Maxwell to make precise mixtures of the colours of the spectrum. Later draft of figures 1-2 found at PT/60/4/3. Subject: Physics Published in Philosophical Transactions as 'On the theory of compound colours, and the relations of the colours of the spectrum'. Communicated by Professor [George Gabriel] Stokes. Received by the Royal Society on 5 January 1860. Read 22 March 1860. [1860]