Davies Gilbert (1763–1833) was one of the most notable figures and an important member of the Cornish scientific community, and had aided Jonathan Hornblower (1753–1815), Richard Trevithick (1771–1833), Arthur Woolf (1766–1837), and Humphry Davy (1778–1829). Since they corresponded a great deal, many historians of science and technology believe Gilbert to be a patron of Cornish engineers.

In 2011, Philip M. Hosken published a book, The Oblivion of Trevithick. Hosken argues that Gilbert did not support Trevithick’s work financially. Gilbert also avoided using Trevithick’s name when he ‘refers to the development of the steam engine in lectures and letters’. Although Hosken remarks on their personal relationship, he does not pay proper attention to their theories of heat and steam.

Davis Baird and David Philip Miller revealed James Watt was not only engineer but also natural philosopher. Watt (1736–1819) believed that heat was caloric by nature. Baird said, ‘elasticity was understood to come from combination of heat—understood as a substance—and water, which together produce the “compound” steam. Watt believed that the pressure in the cylinder affected the ability of the latent and sensible heats in the steam to produce motive power’. At that time, the caloric theory was the most popular theory of heat.

Davy and Count Rumford (1753–1814) had conducted experiments that converted friction into heat. Count Rumford’s article, ‘An Inquiry Concerning the Source of the Heat which is Excited by Friction’, was published in Philosophical Transactions in January 1798. Davy’s article included an experiment that converted friction into heat, ‘Essay on Heat, Light and the Combinations of Light’, was published in 1799, but an original manuscript of Davy’s article preserved at Royal Institution of Cornwall was dated in June 1798. Davies Gilbert knew experiments of Davy and Count Rumford in 1798.

Trevithick made water-pressure engine in Cornwall in 1798. He got the idea for high-pressure steam engines during his time operating high-pressure water engines, and Gilbert encouraged him to invent it. It was possible to adopt the caloric theory to formulate a theory for high-pressure steam engines.

I will discuss Davies Gilbert’s theoretical knowledge of heat and steam and the way scientific knowledge spread among scientists and engineers.

This work was supported by MEXT KAKENHI Grant Number 60447555.