Among the scientific instruments that Horace-Benedict de Saussure improved and  invented was one which he named the Heliothermomètre (solar thermometer), but it is now better known as a hot box. The latter name is a result of its secondary use as a solar oven. He describes how he used it as solar thermometer in Chapter XXXV of "Voyages dans les Alpes". There, he refers his readers to a letter in the Journal de Paris for more details on its development. Two versions of that letter are attached below.  The first, JdP.pdf, is the modern French version transcribed from 18th Century French, and the second,  JeP.pdf, is an English translation. The translation was produced using various computer programs and then corrected by me, Alastair B. McDonald with help from Valerie and Brian Gilligan, then Liz and Norman White.