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. Hoolc.2 -. s. 54 :.

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above 40000 Divisions in a Foot, by the help of two Indexes ; tlie one,fhewing hundreds of Divisioris, the orber Divisions of fhe hundred, evety’lall Division, in my finali one, containing t» of an Inch; and tliat so pre~cifely, that, as I use it, there goes above ii Division; to a Second. Y« 1have taken Land Angles (everal times to one Division, though (for the Rea-iön mentioned by M .Au^out) it be very hard to come to that Exactnels inthe Heavens, vi\. The Swift Motion of the Planets. Yer, to Remedy thatfault, I have Devifed a l{cß, in which I find no sinall Advantage, and not alittle pleasing thoso Persons who have scen it, being so easie to be made, -and'by the Observer manag’d without the help of another ; which lecond Con-venience, my yet Namelesi Instrument halb in great Persection, and is byrcason of its sinallness and shape, ealily applicablc to any Telescope.

z. n n n «, is a sinall oblong Brass Box, serving both to cöntain the Skrewsand its Sockets, or Female Skrews, and also to makc all the soveral moveable °^ YParts of the Instrument to move very True, Smooth, and in a simple Directn.

Motion. To one end hereof is Skrewed on a round Plate of Brass b b b b,about z Inches over ; the extream Limb of whole out-side is divided into ,0 5 -

100 Equal Parts, and numbred by xo, ro, and zo, ( 3 c. Through themid-dle of this Plate, and the rniddle of the Box ana, is placed a very curiousiywrought Skrew of about the bigness of a Goofe-Quill, and of the length ofthe Box, the Head of which is by a fixed Ring or Shoulder on the inside, anda Imall lpringing Plate d d, on the out side, so adapted to the Plate that it isnot in the least sübject to (hake. The other end of this Skrew is by anotherlittle Skrew (whose (mall Points fills the Center or Hole made in the end ofthe longer Skrew for this purpole) rendred so fixt and steady in the Box, thatthere appears not the least danger of (haking. Upon the Head of this Skrew,without the Springing Plate, is put on a sinall Index c e, and above that ^

Handle m m, to turn the Skrew round as often as there (hall be occasion,without at all endangering the dilplacing of the Index, it being put on very • v

stist upon a Cylindrical pan of the Head, and the Handle upon a Squate ' qThe Skrew bath that third of it, which is next the Plate, bigger than theother two thirds of it, by at least as much as the depth of the (mall Skrewmade on it: The Thread of the Skrew of the bigger third is as sinall again,as that of the Skrew of the other two thirds. To the grofler Skrew isadapted a Socket /, fastned to a long Bar or Bolt upon which is fast-ned the moveable Sight b, so that every turn of the Skrew promotes theSight si, either a Thread nearer, or a Thread farther ost trom tfie fixt Sight /.

The Bar gg is made exactly Equal, and fitted into two (mall Staples k. t,which will not admit of any (haking. There are 60 of these Threads; andansiverable thereto, are made 60 Divisions on the edge of the Bolt or Ru-ler gg, and a sinall Index /, fixt to the Box anno, denotes, how manyThreads the edges of the two Sights h and i are distant, ; and the Index e 1,

Ihews on the Circular Plate what pari of a Revolution there is more; everyRevolution, as was sind before, being divided into a 100 Parts. At the fametime that the moveable Sight b is moved forwards or backwards, one or mord F: ^‘Threads of the Courier Skrew, is the Plate f>p, bythemeans of the Socket §,

F 1 1 to