Page:History of the Royal Society.djvu/342

 into which the Terella is half immers'd, till it be like a Globe, with the Poles in the Horizon. Then is the Plane dusted over with steel-filings equally from a Sieve: The Dust by the Magnetical virtue is immediatly figur'd into Furrows, that bend like a sort of Helix, proceeding as it were out of one Pole, and returning into the other: And the whole Plane is thus figur'd like the Circles of a Planisphere.

It being a Question amongst the Problems of Navigation, very well worth resolving, to what Mechanical powrs the Sailing (against the wind especially) was reducible; he shew'd it to be a Wedge: And he demonstrated how a transient Force upon an oblique Plane, would cause the motion of the Plane against the first Mover. And he made an Instrument, that Mechanically produc'd the same effect, and shew'd the reason of Sailing to all Winds.

The Geometrical Mechanics of Rowing, he shew'd to be a Vectis on a moving or cedent Fulcrum. For this end he made Instruments, to find what the expansion of Body was towards the hindrance of Motion in a Liquid Medium; and what degree of impediment was produc'd, by what degree of expansion: with other things that are the necessary Elements for laying down the Geometry of Sailing, Swimming, Rowing, Flying, and the Fabricks of Ships.

He has invented a very curious and exceeding speedy way of Etching. He has started several things towards the emendation of Water works. He has made Instruments of Respiration, and for straining the breath from fuliginous vapours, to try whether the same breath so purify'd will serve again.

He was the first Inventor of drawing Pictures by Microscopical Glasses. He has found out perpetual, at Rh