Paper, 'On the thermodynamic properties of substances whose intrinsic equation is a linear function of the pressure and temperature' by George Francis Fitzgerald Fitzgerald writes: 'Professor [William] Ramsay has communicated to me that he and Mr [Sydney] Young have found that within wide limits several substances in the liquid and gaseous states have the following relation connecting their pressure (p), temperature (T), and specific volume(v), p = aT + b, where a and b are functions of v only. Now in this case the following are the forms that the thermodynamic equations assume. T is temperature, and ϕ is entropy, and c and e are functions to be investigated, c being = dl/dT, where I is the internal energy, and e = dl/dv.' Annotations in pencil and ink throughout. Subject: Thermodynamics Received 11 January 1887. Read 27 January 1887. A version of this paper was published in volume 42 of the Proceedings of the Royal Society as 'On the thermodynamic properties of substances whose intrinsic equation is a linear function of the pressure and temperature'. 1887