I was trying several small and single Magnifying Glasses, and casually viewing a parcel of white Sand, when I perceiv’d one of the grains exactly shap’d and wreath’d like a Shell, but endeavouring to distinguish it with my naked eye, it was so very small, that I was fain again to make use of the Glass to find it; then, whilest I thus look’d on it, with a Pin I separated all the rest of the granules of Sand, and found it afterwards to appear to the naked eye an exceeding small white spot, no bigger than the point of a Pin.  Afterwards I view’d it every way with a better Microscope and found it on both sides, and edge-ways, to resemble the Shell of a small Water-Snail with a flat spiral Shell:  it had twelve wreathings, a, b, c, d, e, &c. all very proportionably growing one less than another toward the middle or center of the Shell, where there was a very small round white spot.  I could not certainly discover whether the Shell were hollow or not, but it seem’d fill’d with somewhat, and ’tis probable that it might be petrify’d as other larger Shels often are, such as are mention’d in the seventeenth Observation.

* * * * *

Observ.  XII. Of Gravel_ in Urine._

I Have often observ’d the Sand or Gravel of Urine, which seems to be a tartareous substance, generated out of a saline and a terrestrial substance crystalliz’d together, in the form of Tartar, sometimes sticking to the sides of the Urinal, but for the most part sinking to the bottom, and there lying in the form of coorse common Sand; these, through the Microscope, appear to be a company of small bodies, partly transparent and partly opacous, some White, some Yellow, some Red, others of more brown and duskie colours.

The Figure of them is for the most part flat, in the manner of Slats or such like plated Stones, that is, each of them seem to be made up of several other thinner Plates, much like Muscovie Glass, or Englsh Sparr to the last of which, the white plated Gravel seems most likely; for they seem not onely plated like that, but their sides shap’d also into Rhombs, Rhomboeids, and sometimes into Rectangles and Squares.  Their bigness and Figure may be seen in the second Figure of the seventh Plate, which represents about a dozen of them lying upon a plate ABCD, some of which, as a, b, c, d seem’d more regular than the rest, and e, which was a small one, sticking on the top of another, was a perfet Rhomboeid on the top, and had four Rectangular sides.

The line E which was the the measure of the Microscope, is 1/32 part of an English Inch, so that the greatest bredth of any of them, exceeded not 1/128 part of an Inch.

Putting these into several liquors, I found oyl of Vitriol, Spirit of Urine, and several other Saline menstruums to dissolve them; and the first of these in less than a minute without Ebullition, Water, and several other liquors, had no sudden operation upon them.  This I mention, because those liquors that dissolve them, first make them very white, not vitiating, but rather rectifying their Figure, and thereby make them afford a very pretty object for the Microscope.