If an artificial eye were truly and dioptrically made (which I would have at least 3 inches diameter) it would represent the picture, as nature paints it. The Cornea and Chystalline must be glas, the other humors water. I once surveighed an horses eye as exactly as I could, measuring what the diameters of the severall spheres of the Humors were, and what the proportions of the distances of the centers of every sphericall superficies was upon the Axis of the Eye. The wayes, by which I did it, are too long to rehearse; but the projection in treble the magnitude Sir P. Neile may possibly find; or, if your Lordship think it worthwhile, I shall reiterate the Experiment.
A Needle, that would play in a Coach, will be as usefull to know the Coast and way (Joyned with the way-wiser) as a pleasant diversion to the Travailer, and would be an acceptable present to his Majesty, who might thus, as it were, sayle by land. The Fabrick of it may be such as this: In a sphere of Glasse of 2 inches diameter, half full of water, cause a short broad heavy needle to swim, being boyed up by the Chart, and both varnished: instead of a Cap and Pin, let the perforated needle play about a smal wire or horse haire, extended like a perpendicular Axis in the Glas-sphere; which being made weighty with Lead, fixed to the Nadir, and a Horizon as it were cemented to it, let it play in circles, like the vulgar compasse. Then let a Hemisphericall Concave-box, containing the sphere in its circles be hung upon springs after this manner. Suppose a basis, upon which are erected perpendicularly 3. stiffe woodden springs of yew; from the Ends of which springs are strings or nerves strained, forming an equilateral triangle, the midle of whose sides passe through 3. small loopes on the brim of the Concave, which therefore hanging on the Lutestrings represents a circle inscribed in a Triangle: from the midle of the basis ariseth a worme spring fastned by a spring to the Nadir of the Concave, drawing it down a litle, and acting against the other 3. springs. Thus I suppose the springs will take much of the laterall and perpendicular concussions; the circles will take of Oscillations; the Agitations remaining will be spent in the water, and stilled by the Chart covering the superficie of the water; for thus we see a Trencher swimming in a bucket keep the water from spilling in carriage. And the Chinese instead of Circles have their compas swimming in water. Lastly, I would have at the bottom of the basis near the edge made like a brush, but with soft thick and inclining bristles, which will ease it like 1000. springs. It should be placed on the midle of the floore of the Coach, where by opening a window you may likewise see the waywiser placed on the pearch.
My Lord, if my first designs had been perfect, I had not troubled your Lordship with so much scrible, but with something performed and done, but being taken of by my occasions, I had rather be impertinent than disobedient, and am fain in this letter to do like the common Chymist, who, when projection (his fugitive darling) hath left him thredbare, is fain to fall to vulgar preparations to pay his debts. And I must needs acknowledg, I am not only indebted to the Society and most particularly to your Lordship, to whom I ow a double duty, both as to our President and to my very good Lord and Patron.
O.B.C. July:30:1663