go

Optics.

pended, moveable about its Axis by means of two

Screws at a a. This Frame is fixed to the Pie ce

• • Jt*jC

which being hollow is moveable upon the cyl^)Shaft P about the Iron Pin e. (See the Part by aThis Pillar P is fixed to a triangular Base or F° otperpendicular by the three Screws B, B, B. , }

21. On the Back-part of the Speculum is fix^long cylindric Wire or Tail D, in a perpendicularfition. By this it is connected to the second Pa^^the Heliojlata , which is a common Thirty-Hour Cl 0 ^represented at H ; the Plane of which Clock is p al ^ £to that of the Equator in any given Place. This Cl° j {is sustained on .the Column F G, in which it is moy ea s jup and down by a thin Lamina or Plate that enters it ^Cafe, and fixed to a proper Height by the Screws ^at the Side. The Whole is truly adjusted to a P er E 5 J tdicular Situation by means of the three Screws I, j.in the Tripod LL M, and the Plummet Q_,

Cuspis must answer to the Point o beneath.

22. The Axis of the Wheel, which moves thedex N O over the Hour-Circle, is somewhat large ? i .perforated with a cylindric Cavity verging a little t .conical Figure ; and receives the Shank p q of the > (Index N O very close and tight, that by its Moti ofl JIndex may' be carried round. In the Extremity y,^ { ■the Index is a small cylindric Piece n, with a cyl* ,lsl fiPerforation to receive the Tail t of the Fork T, u

: of ,

as to admit a free Motion therein. In each Side 1

t,eh

Fork are several Holes exactly opposite to each otin which go the Screws r, r, upon whose smooth jblindrjc Ends moves the tubular Piece R on its Auh cm, m. ..

23. When the Machine is to be fixed for Use, jj’j

ther Part is made use of to adjust it; which is c ^rp,the Pofttor, and is denoted by the Letters V X * j,jT he Cylinder C is removed with the Speculum fro? 1 J,Foot P, and the Brass Column V X put on in itsand adheres more strictly to the Pitt e, that it may *its Position while the Machine is constituted, 3

24. On the Top of the Column, about XCentre, moves the Lever Y Z, so that it may behpw inclined to the Horizon, and keep its Po^j,s