"( 19 ° )

' Glass is piaced so much distant from the Focus of the first Eye Glast, as is tli CFocus of this middle Eye Glast ; lastly,the nearest Eye Glass is piaced fo muchdistant from the Focus of this middle Eye Glass, as is the Focus of this nearestEye Glaß ; and the Eye looking through them all is piaced 1 in the Focus ofthis nearest Eye Glass.

I say therefore, i.That oae single Convex Glast, cannot properly be stidbyit seif to sliew Objects Erect or Reverse, but in respect of placing of the Eyethat looks through it. For if the Eye, that looks through a fmgle ConvexGlast, be piaced nigher thereto than the Glaß’s Focus, the Objects are Erect ;if the Eye be piaced just in the Focus, the Objects are neither Erect nor Re-vcrscd, but all in Confusion between both ; and if the Eye be piaced furtlierfrom the Glass than the Focus, the Objects areReversed. I mean here distantObjects, the Rays flowing from any Point whereof may be counted to comeParallel towards the Object Glast.

a. The Object Glass of a Teleskope reverses the Object, both to the EyeGlals and the Eye, that looks through it: For the Eye Glast is.piaced’farther-from the Object Glast than is the Focus of the Object Glast. But the Eye

■ Glast docs nothing tov/ards the Rectification, or Reversion • the Eye bringpiaced just in its Focus.

z. If the second Eye Glast sthe first being that next the Object Glass) be.piaced as it ought in a Teleskope, Place the Eye nearer to this middle EyeGlals than its Focus, and it sees the Objects Inverted and Confused : Place the >,Evc in the Focus, and it sees the Objects all in Confusion, neither Erect nor Rc-vetsed ; for here again there is a distinet Representation of the Objects to bc■received on a piece of Paper, as in the Focus of the Object Glast, and theEye bcing piaced at any time at this place (wbich is usually-calfd the Distinet hBase) sees all in Confusion : But then let the Eye be piaced farther from thismiddle Glass than its Focus, and it perceives the Objects Erect and Confused.

, Lastly, The third,or immediate Eye Glast, does nothing towards theErectingorReveriing the Species,which it receives Erect from the middle Eye Glast ; nomore than in a Teleskope of two Convex Glafles, the Eye Glast does to theSpecies it receives from the Object Glast, as v/e have shewn before. Therei-lon that this last or immediate Eye Glast ; has nothing to do in the Erecting ,or Reversing the Species, is the sime, as in a Teleskope of two Convex Ghl- |sis, vt\. The Eye is piaced in its Focus, and therefore fees the Species as 'tu ;reprefented in the distinet Base ; that is, the Species is Inverted in the distine: ;Base of the Object Glast, and therefore a single Convex Eye Glast brings it tothe Eye Inverted ; but in the distinet Base of the middle or second Eye Glass

■ the Species is Erect, and therefore the third or immediate Eye Glast brings itto the Eye Erect.

Wherefore we are to confider the Teleskope consisting of an ObjectGlass and three Eye Glafles, as two Teleskopes, each consisting of two Con- ‘vex Glafles. The first. consists of the Object Glast and first Eye Obs-,

. and this Inverts the Species, that is, the Species is Inverted in the Distinet Basiof the Object Glast, and Io brought into the Eye. The second Teleskope iconsists of the two immediate Eye Glafles, and this Erects what the former ln-.verted , that is, the Species in the Distinet Base of the middle Eye Glass n

Erect,