X07.

108.

( )

ta which it is Skrewed, movcd forward or backward, one or more threads cfthe finer Skrew: So that this Piate, bcing fixt to thc Teleseope by theSkrews r r, lo as the middle bctwixt the Sights may lic in the Axis of thcGlast, however the Skrew be turned, the midst betwixt the Sights will al-ways be in the Axis, and the Sights will equally eithcr Open from it, or Shutrowards it.

It is coaceived by some Ingenious Men, that it will be more convenient,-instead of the edges of the two Sights b and 1, to employ two Sights r and s,futed with the Hairs t and v, lb that they may be conveniently uled. in the.place of the solid edges. of the Sights b and

The Instrumentis thus applied to the Tclefcope; The Tube AD is di-,vided into three lengths,. of which (as in ordinary ones) BC is to Lengthen,or Contra cf, as the Object requires : But A B is here added, that at A yemay put such Eye Glasses, as {hall be thought most convenient, and to let.them stili at the Distance most proper from thc Indexes, or Pointers, whichhere are supposod .to be at B,. which length. alters also in relppct of diversPerlons Eyes, E is a Skrew, by which thc great. Tube can be sixt so, as.by the help of the Figures any Imaller part of it can immediately be found,measuring only, or knowing the Divisions on B C, thc Distance of the Ob-,ject Glast from the Pointers. F is the Angular picce.of Wood, that lies on.the upper Skrew of the Rest.

This Rest, ( by Dr. Hool £s Suggestion ) may be rendred more conveni-ent, if, instead of placing thc Skrew Horizontal, it bc so contrived, thatit may be laid Parallel to the Equinoctial, or. to the Diurnal Motion of theEarth; for, by that means, the fame thing may be performed by. the sin-,gle Motion of one Skrew, which in the other way cannot be ,donc but by,the turning of both Skrews; as will casily appear to.thole that {hall consi-det it. .

3. I have by me .two or tliree several ways of Measti ring the Diametersof the Planets, whether Horizontal, Perpendicular, or Inclined, to die Exact-nefs of a Second, by the help of a Telesoope: as also, of taking, the. Posi-tion, and Distance of the small fixt Stars one from, another, or from any o£n.23. t- 459- the lest brjght Planets, if the Distance be. not, above two or three De-,grees. ,

SxtiUe?xe cftbe 4- Micrometro.Lc Tubo Pedum 14, Planetarum frequenter DiametrosMurcm<ter\ by Fixis Distantias, ad Secundos fer,e Scrupulos, quod vix inexpertus credes,Afr.Hair.stecd. J)i men so s som..

N.FÜ. f. 6099■ .

TUin sühn re- VI. i. .Pluribus Argumentis evinci potest, Tyclxmnn siepe cum in Locis,jtifeJ-, by tum Latitudinibus, Fixis quibusdam aisignatis, duos trefve & interdum qua-,Mr.Flamstced. tuor „ut quinciue totos Scrupulos a vero aberrasse._ Fixarum quidem Resti-

st. p^» f» K II y • - 1 'I , 1 1 * A

a..LK. f. tiico. tutionem lulcepille Celcberriuna Jonnnem Hcrjchum. audrvmms, attamen quan-doquidem Pinacidiis Vitrorum Callis fertur.ipsum uti* dubium an multumah ipso Emendatiores. Locos habituri Iimus quam reliquit Tjcho., nisi. ubivaj.de hullucinatus est.

r-iF. 109.

Jbid , f . 55 6 *

Oiftunctty tu-itmxieti ; by ■Dr. Hook.

2. Per