point, but Poggendorff says he made no application of this fact to thermometry. Halley thought that "spirit of wine" lost part of its expansive force by long keeping, yet he proposed the boiling-point of alcohol as a limit to thermometrical scales. The English scientist felt the need of a reliable thermometer scale and expressed himself in somewhat the same way as his countryman Boyle had done, fourteen years before: "I cannot learn that any thermometer of either sort was ever made or adjusted so as it might be concluded what the degrees or divisions of the said instrument did mean; neither were any thermometers ever otherwise graduated but by standards kept by each particular workman without any agreement or reference to one another. So that whenever observations of a thermometer are made by any curious person to signify the degree of heat in the air or other thing they cannot be understood, unless by those who have by them thermometers of the same make and adjustment."
Halley regarded the freezing-points of aniseed oil, and of water, as unreliable, and preferred as a starting point the temperature of a deep cellar the constancy of which had been de-
