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 Secondly, from our feeling a greater cold than what is observable in the weather-glass (instrumentum temperatorum). For the moisture or ponderousness of the air is to us the measure of its coldness. Thirdly, from the greater or lesser bending of a very thin board, especially if it be of a pear tree. Fourthly, from the contraction of the strings of a lute, or from hemp." (Section II, Aphorism IV, English translation by J. D., London, 1678.)

In this "aphorism" Sanctorius mentions three hygroscopes and one thermoscope. Parenthetically, I call attention to the use of burnt alum and of a balance to determine atmospheric moisture quantitatively.

The thermoscope used by Sanctorius is described by him in his "Commentaries on the first section of the first book of Avicenna," printed at Venice in 1646. In the preface to this the author says he has been engaged for fifteen years in preparing descriptions of his instruments, but the publication has been