Prepare (_saith he_) two Glasses, the one exactly flat on both sides, the other flat on the one side, and convex on the other, of what Sphere you please. Let the flat Glass be a little broader than the other. Then let there be made a Cell or Ring of Brass, very exactly turn'd, into which these two Glasses may be so fastened with Cement, that the plain surfaces of them may lye exactly paralell, and that the Convex-side of the Plano-convex-Glass may lye inward; but so, as not to touch the flat of the other Glass. These being cemented into the Ring very closely about the edges, by a small hole in the side of the Brass-ring or Cell, fill the interposed space between these two with _Water_, _Oyl of Turpentine_, _Spirit of Wine_, _Saline Liquors_, _&c;_ then stop the hole with a screw: and according to the differing refraction of the interposed Liquors, so shall the _Focus_ of the compound Glass be longer or shorter. But this (adds the _Proposer_) I would only have look't upon, as one instance of many (for there may be others) of the _Possibility_ of making a Glass, ground in a smaller Sphere, to constitute a Telescope of a much greater length: Though (not to raise too great exspectation) I must add, That of _Spherical_ object glasses, those are the best, which are made of the greatest Sphere, and whose substance hath the greatest refraction. * * * * * _Observations about _Shining Worms_ in Oysters._ These Observations occur in the _French journal_ of _April_ 12. 1666. in two letters, written by M. _Auzout_ to M. _Dela Voye_; whereof the substance may be reduced to the following particulars. 1. That M. _Dela Voye_ having observed, as he thought, {204} some shining Worms in Oysters; M. _Auzout_, being made acquainted with it, did first conceive, they were not Worms (unless they were crushed ones) that shin'd, as having not been able then to discern any parts of a Worm; but only some shining clammy moysture; which appeared indeed like a little Star of a blewish colour, and stuck to the Oyster-shell; being drawn out, shone in the Air its whole length (which was about four or five lines,) and when put upon the _Observers_ hand, continued to shine there for some time. 2. That M. _Auzout_ afterwards, causing more than 20. douzen of Oysters to be open'd at Candle-light, really saw, in the dark, such shining worms in them; and those of three sorts. _One_ sort was whitish, having 24. or 25. feet on each side, forked; a black speck on one side of the head (taken by him for a _Chrystallin_) & the back like an Eele, stript off her skin. The _second_, red, and resembling the common _Glow-worms_, found at Land, with folds upon their backs, and feet like the former; and with a nose like that of a dog, and one eye in the head. The _third_ sort was speckled, having a head like that of a Sole, with many tufts of whitish hair on the sides of it,