text: Gibbs papers defined what Gibbs called the "thermodynamic surface," which expressed the relationship between the volume, entropy, and energy of a substance at different temperatures and pressures. However, Gibbs did not include any diagrams of this surface. After receiving reprints of Gibbs papers, Maxwell recognized the insight afforded by Gibbs new point of view and set about constructing physical three-dimensional models of the surface. This reflected Maxwells talent as a strong visual thinker and prefigured modern scientific visualization techniques.
  Maxwell sculpted the original model in clay and made several plaster casts of the clay model, sending one to Gibbs as a gift, keeping two in his laboratory at Cambridge University. Maxwells copy is on display at the Cavendish Laboratory of Cambridge University, while Gibbs copy is on display at the Sloane Physics Laboratory of Yale University, where Gibbs held a professorship. Two copies reside at the National Museum of Scotland, one via Peter Tait and the other via George Chrystal. Another was sent to Thomas Andrews. A number of historic photographs were taken of these plaster casts during the middle of the twentieth century – including one by James Pickands II, published in 1942 – and these photographs exposed a wider range of people to Maxwell's visualization approach.