Amongst all the experiments pneumaticall, there is none more excellent than this of the Weather-glasse: wherefore I haue laboured to describe the making thereof as plainly as it possibly might be.
What the Weather-glasse is.
A Weather-glasse is a structure of, at the least, two glasses, sometimes of three, foure, or more, as occasion serueth, inclosing a quantity of water, and a portion of ayre proportionable, by whose condensation or rarifaction the included water is subject unto a continuall motion, either upward or downward; by which motion of the water is commonly foreshewn the state, change, and alteration of the weather. For I speak no more than what mine experience hath made me bold to affirme; you may (the time of the yeere, and the following obseruations understandingly considered) bee able certainly to foretell the alteration or uncertainty of the weather a good many houres before it come to passe.
Of the severall sorts and fashions of Weather-glasses.
There are diuers seuerall fashions of Weather-glasses, but principally two.
1 The Circular glasse.
2 The Perpendicular glasse: The Perpendiculars are either single, double, or treble.
The single Perpendiculars are of two sorts, either fixt or moueable.
The fixt are of contrary qualities; either such whose included water doth moue upward with cold, and downward with heat, or else upward with heat, and downward with cold.
In the double and treble Perpendiculars, as the water ascendeth in one, it descendeth as much or more in the other.