lOt) PHILOSOPHICAL TRANSACTIONS. [aNNO IOQJ. 



On an Optic Lots of IT'itter, for viewing loth near and distant Objects, with the 



Description of a Natural Reflecting Microscope. By Mr. Stephen Gray. 



N° 228, p. 539. 



I send you here a short account of what has been the success of my attempts, 

 to make small portions of water subservient to the viewing both near and dis- 

 tant objects, together with the description of a natural reflecting microscopt;. 



Drops of fair water being let fall on a piece of plain glass, form themselves 

 into piano con vexes, having a convexity proportionable to the height, from 

 which they descend, viz. from a greater height a less, and from a less hiight a 

 greater degree of convexity. I applied some of these as reading glasses for 

 single words of small letters, as on the globes and maps, and found no other 

 inconveniency, than that the fluidity of the water obi ges one to keep the glass 

 horizontal, which I remedied thus: I took a sufficient quantity of isinglass, 

 and dissolved it in water over the fire; and whilst it was warm I dipped a stick 

 into the solution, and let some drops of it fall on the glass as before, and in a 

 quarter of an hour they acquire a consistency that permits them to be held in 

 any pobition ; and though they are not quite so transparent, yet this is little or 

 no impedunent to their use. The drops of this solution are more exactly defined 

 than those of common water, having their edges exactly circular, and one may 

 make them of a much longer focus. 



A thin flat ring of brass, not exceeding -jSA''-^ of an inch diameter in its in- 

 terior circle, being cemented to a plain piece of glass, and filled with water, or 

 the solution above-mentioned; then by pressing the finger into it, till what is 

 superfluous be taken off, there will be formed a piano concave, which may serve 

 as an eye-glass to a prospective, or to any other optical use concave glasses are 

 applicable to. 



I have tried whiit would be the success of combining jjortions of water by 

 the help of brass rings, and plain pieces of glass, to give them their true figure 

 and requisite apertures, autl inserted them at tlic ends of tubes of several 

 lengths, and find, that though these natural lenses may serve as eye-glasses, 

 yet when used as object ones, either to telescopes or double microscopes, their 

 efiects will not compensate the trouble there is in using them. 



For the reflecting mieioscope, a, fig. 1, pi. A, represents a small fiat ring of 

 brass, whose interior circle must not much exceed -rV^'i^ ^^ ^" \nc\\ diameter, 

 and about -^'-^Xh of an inch thick ; this we may call the frame or cell of the glass; 

 it must be prepared for use after the following tnanner : Take a sniall globule 

 of quicksilver, and dissolve it in a few drops of aquafortis, to which you may 

 add ten parts of common water; dij) the end of a stick in this liquor, and rub 



