“The author [Davy] derived no assistance whatever from the Count’s ingenious labours. My first knowledge of him arose from a letter written in April 1798, containing an account of his researches on heat and light; and his first knowledge of Count Rumford’s paper was conveyed by my answer. The two Essays contain proofs enough of an original mind to make it credible that the simple and decisive experiments on heat were independently conceived. Nor is it necessary, in excuse or in praise of his system, to add, that, at the time it was formed, the author was under twenty years of age, pupil to a surgeon-apothecary, in the most remote town of Cornwall, with little access to philosophical books, and none at all to philosophical men.” Having thus, with Beddoes, expunged caloric from his chemical system, Davy proceeds to elevate the matter of light into its place. According to Lavoisier oxygen gas was a compound of a simple substance and caloric; Davy seeks to show that it is a compound of a simple substance and light. He objects to the use of the word “gas,” since, according to French doctrine, it is to be taken as implying not merely a state of aggregation but a combination of caloric with another substance, and suggests therefore that what was called oxygen gas should henceforth be known as _phosoxygen_. His “proofs” that oxygen is really a compound of a simple substance with “matter in a peculiar state of existence” are perhaps the most futile that could be imagined. Charcoal, phosphorus, sulphur, hydrogen, and zinc were caused to burn in oxygen; _light_ was evolved, oxides were formed, _and a deficiency of weight was in each case observed_. He regrets, however, that he “possessed no balance sufficiently accurate to determine exactly the deficiency of weight from the light liberated in different combustive processes.” “From these experiments, it appears that in the chemical process of the formation of many oxyds and acids, light is liberated, the phosoxygen and combustible base consumed, and a new body formed.... Since light is liberated in these processes, it is evident that it must be liberated either from the phosoxygen or from the combustible body.... If the light liberated in combustion be supposed (according to Macquer’s and Hutton’s theories) to arise from the combustible body, then phosoxygen must be considered as a simple substance; and it follows on this supposition, that whenever phosoxygen combines with combustible bodies, either directly or by attraction from any of its combinations, light must be liberated, which is not the case, as carbon, iron and many other substances, may be oxydated by the decomposition of water without the liberation of light.”