From Newton's note-books it appears that he was occupied with these studies in March, 1692-3, although they were not made public until 1701.
Newton made no use of the boiling-point of water in constructing his scale of temperatures, as he considered it variable; he recorded that water begins to boil at 33° of his scale, and boils vehemently at 34° to 34½°. We now know that such fluctuations depend upon the position of the thermometer (which must not be immersed in the liquid), on the pressure of the atmosphere, on the chemical purity of the water, and on the shape of the vessel holding it, so it is not surprising that doubts existed as to the constancy of the phenomenon. Mariotte had laid the foundations of hypsometry, but the experimental proofs were not secured until Le Monnier tested the matter in the Pyrenees in 1739.
In the same year that Newton published his researches, Étienne François Geoffroy described an open air-thermoscope nearly identical with that of Athanasius Kircher, made in the year 1643, and to which the French savant made no allusion. (Phil. Trans., 1701, p. 951.)