C543) 
Other tw& Thirds oi by atleaftas much as th« depth of the 
fmall Screw y made on it: The thred of the Scntv of the bigger 
Thirdls as fmall again,as that of the Screw of the other two Thirds. 
T o the grojfer Screw is adapted a Socket (f) faftned to a long 
jBarr or Bolt ( gg^ ) upon which is faftned the Moveahle Sight {h^) 
fo that every turn of the Screw promotes the Sight Qh) either a 
thredn^^xtv^ or a thred farther off from the fixt Sight (i ) The 
Barr (gg ) is made exadly equal and fitted into two fmall Staples 
(kk') which will not admit of any {baking. There are do cfthefe 
threds'j and^ anfwerable thereto, are made 60 divifions on the 
edge of thtBolt or Ruler^gg-^ ) anda fmall Index (/) fixt to the 
Boxe (a a a) denotes^ how many threds the Edges of the two 
Sights ( ^ ) and ( i ) are diftant 5 and the Index {ee) fhews 00 
the Circular Plate, what part of a revolution there is more every 
revolution, aswasfaid before, being divided into ico parts. At 
the fame time that the moveable Sight (h) is moved forwards or 
backwards, or more threds of the Courfer Screw, is the Plate 
(fp,inFig.2j by the means of the Socket (^q) to which it is 
fcrew'd, moved forward or backward^^or more threds of the finer 
Screw: So that this Plate^ being fixt to the Telefcope by the 
Screws ( rr. in fig. 2, ) fo as the middle betwixt the Sights may 
lye in the J xis of the Glafs^ however the Screw be turn'd^ the 
midft betwixt the Sights will always be in the Jxis,znd the Sights 
v/ill equally either open from it, or fhut towards ic. 
Figure 2. reprefents the moveable Ot/^r containing the Screm '^ 
to be by the Bookfeller cut off, by the pricked Line (^xxx)ixQm 
the Paper, and to be fitly placed on Figure i. according to the 
pricked Line fj'^'j; ) anfwering thereto-, that by the taking oflF, 
as it were, or folding up of this Cover^ the //^jr^r^ contrivance 
of the Screws znd Sight smdiY 2.^^ezx. 
And becaufe it is conceived by fome ingenious men, that it will 
be more convenient , inftead of the Edges of the two Sights 
( h and i) to employ two Sights fitted with hairs, therefore is add- 
ed Figure 3, reprefenting tht tv^o Sights (r. andj.) fo fitted 
with threds ( t, and u, ) that they may be conveniently us'd in the 
place of the [olid Edges of the Sights ( h, and /. ) 
The Figure reprefents, How t\\t Screws are to be put on.' 
Kkk 2 The 
