Theatrum naturae et artis

(f.) Which is indicated by hygroscopes instruments for measuring humidity, which are generally wont to be constructed from cords, either natural or artificial. I observe the natural ones in oats, and these are very sensitive, by which an index placed upon them is easily turned to the degrees marked in a circle. To the artificial ones I refer ropes and strings usually applied to musical instruments, and from the class of these I show various hygrometers moisture-meters, which are the same in reality and vary only in construction. Others can also be fashioned from wool, brought first to equilibrium on a balance scale: by placing certain types of salts on the pan of the scale: from various woods, and so on. There is also another composed like a scale for the hands, from one arm of which hangs a glass globe, and from the other an equal weight; a pointer indicates the degrees on a semicircle.

Finally, a small machine is submitted showing the combination of various thermometers and hygrometers.

On Water.

I.

(a) By means of a special level, divided into its own degrees, which, when immersed in liquids, indicates their relative purity by its descent.

Before we descend to hydraulic principles, regarding the assessment of the purity and impurity of water and other liquids: (a) regarding the equal weight original: "æquiponderantia" of fluids according to height, (b) not according to bulk: and the phenomena of narrow channels are set forth as a preface.