Page:History of the Royal Society.djvu/197

Rh

OR the better making a History of the Weather, I conceive it requisite to observe,

"1. The Strength and Quarter of the Winds, and to register the Changes as often as they happen; both which may be very conveniently shewn, by a small Addition to an ordinary Weather-cock.

"2. The Degrees of Heat and Cold in the Air; which will be best observed by a sealed Thermometer, graduated according to the Degrees of Expansion, which bear a known Proportion to the whole Bulk of Liquor, the beginning of which Gradation, should be that Dimension which the Liquor hath, when encompassed with Water, just beginning to freeze, and the Degrees of Expansion, either greater or less, should be set or marked above it, or below it.

"3. The Degrees of Dryness and Moisture in the Air; which may be most conveniently observed by a Hygroscope, made with the single Beard of a wild Oat perfectly ripe, set upright and headed with an Index, after the Way described by Emanuel Magnan; the Conversions and Degrees of which may be measured by Divisions made on the rim of a Circle, in Rh