Miscellanea Curiosa, Vol. 1 / Containing a collection of some of the principal phaenomena in nature, accounted for by the greatest philosophers of this age

by Unknown

1. For the Art of Producing Light, we have the Frication of all hard Bodies that beget Fire; especially of the Flint and Steel; and instead of the Flint, most hard Stones (as well as the Cane) may be us'd to the same effect, as upon trial I have found. Add hereto the lately invented Phosphorus, which is a new and admirable way of producing a Lucid Substance by Art, out of a Body in itself not Lucid; and therefore may not unfitly be term'd an Artificial production of Light.

And then of the Art of Conserving Light, the Lapis Bononiensis is a notable Instance; and so happily were the Sepulchral Lamps of the Ancients.

2. As to Colours, 'tis the greatest part of the Art of Dying to be able to make and fix (that is preserve) them; and the Painters and Limners will own it to be no small part of their Skill to be able well to Mix (that is, in effect, to Generate) Colours.

3. For Imitation of Light and Colours, 'tis well known how far Perspective with the Art of Limning and Shadowing have gone therein, which all tend some way to the Advance or Improvement of Direct Vision.

Add to all these, That a due Application of Light to the Object renders it Visible, if it were not so before; as appears from a dark Room illuminated; or else makes it better and more truly discernable by the Sense of Seeing, if before it might have been discern'd.

Hence the same Colour, in a diverse Light, will appear different, and no Picture can well be discern'd or judg'd of but by its true Light. Besides, the Limner will assure you, that he can hardly make true Work, or hit the Air of a Face exactly, unless he draw by a North-Light, by reason of the steadiness of that, and the uncertainty of all other Lights whatsoever. Which things shew, that the Art of duly applying Light to the Object does very much help and improve Vision. So also does the due placing of the Object, as to Height and Distance. But to enumerate all things that help Direct Vision, would be infinite.

2. Ex parte Organi vel Medii, Direct Vision has been improv'd by making use of a Tube, without Glasses, or a Man's clos'd Hand, to look thro'; which admitting into the Eye only the principal Rays, that come directly from the Object, do very much strengthen and clear the Sight, by excluding all the Collateral Rays, that crouding into the Eye, together with the direct ones, would confound and disturb it, partly by mixing and interfering with the direct Rays, and partly (or rather chiefly) by too much enlightning the fund of the Eye, wherein Vision is truly (tho' then imperfectly) made.

On this is founded the Art of making Spectacles without Glasses; (as well as Tubes) which is done by putting into the Glass-holes (instead of Glasses) two short Tubes of between three and four Inches long (for their length is to be vary'd according to the Age or Eye of the Beholder, and so also is the Diameter of the extream ends) which Tubes being made of Spanish Leather (or Past-board, or some such like Matter) and black'd on the inside, are so to be placed, as that the visual Rays, receiv'd thro' them, may meet in one point (or rather issue out from one Point) of the Object standing at such a due distance, as the Person may clearly and distinctly see it, or according to his length of Sight (as ABC, in the 4th Fig. Tab. 3.)

And these Spectacles may be suppos'd better for preserving the Sight, than the ordinary ones with Glasses, because they represent the Object more naturally, and withal more clearly and distinctly to the Eye, than the other, whose refracted Rays being collected together with the right ones in the Glasses, do somewhat confound good Vision, as before: Especially if the visive Power be strong enough to be sufficiently determin'd by the right Rays alone.

For I speak now of preserving a good Eye by these Spectacles, which holds in proportion true also of a bad one. Because those Rays (both right and refracted) being collected and brought so near the Eye (whether good or bad) as the Spectacles are usually plac'd, do too much affect it, both by their own brightness, and also by the brightness of the Colours of the Object (when they are bright) which is brought very near also; whereby the Eye is dazl'd and confounded, unless there be a strong attention and conatus of the Spirits, whereto the bright Rays do certainly engage them, which of necessity weakens Vision, especially if these Glass-spectacles be much us'd.