The discovery of latent heat 250 years ago

The concept of latent heat plays an important role in the description of the energy balance of the Earth's atmosphere. It is a quarter of a millennium ago that J.A. DELUC began his experiments on melting ice. He discovered that during the melting some heat is concealed in the water without affecting the thermometer. Some years later J. BLACK coined the term 'latent heat' for this phenomenon. Thirty-two years later DELUC discussed with J. WATT the question of who should be credited for this discovery. Excerpts from a book by DELUC, from the manuscripts of BLACK's lectures and from a letter by WATT illustrate the topic. WATT's letter and DELUC's reply to it are an early example of what is found today in the 'Letters to the Editor' section of scientific journals.