References 1. (a) Gibbs, J. Willard. (1873). "Graphical Methods in the Thermodynamics of Fluids" (pg. 3), Transactions of the Connecticut Academy, I. pp. 309-342, April-May. (b) Clausius, Rudolf. (1879). The Mechanical Theory of Heat(pg. 68).London: Macmillan & Co. References 2. Maxwell, James. (1875). “Letter to James Thomson”, July 8th; in The Scientific Letters and Papers of James Clerk Maxwell (pgs. 230-31).Volume 3; 1874-1879.