330 PHILOSOPHICAL TBANSACTIONS. [aNNO iSsS. 



versed. I mean here by distant objects, the rays flowing from any point of 

 which may be counted to come parallel towards the object-glass. 



Secondly, the object-glass of a telescope reverses the object, both to the eye- 

 glass and the eye that looks through it : for the eye-glass is placed farther from 

 the object-glass than is the focus of the object-glass. But the eye-glass contri- 

 butes nothing towards the rectification or reversion, the eye being placed just 

 in its focus. Thus we see that the reversion of objects, in a telescope of two 

 convex-glasses, proceeds wholly from the object-glass and its position ; and the 

 eye-glass has no concern in the effect ; for were the eye itself in the place of 

 the eye-glass, it would see the objects inverted through the single object- 

 glass. 



To come now to consider the second eye-glass placed after the first, which 

 is that next the object-glass : it is here manifest, that if we place our eye 

 nearer to this middle eye-glass than its focus, the eye sees the object inverted 

 and confused : place the eye in the focus, it sees the objects all in confusion, 

 neither erect nor reversed ; for here again there is a distinct representation of 

 the objects to be received on a piece of paper, as in the focus of the object- 

 glass ; and the eye, being situated at any time at this place, which is usually 

 called the distinct-base, sees all in confusion. But let the eye be placed farther 

 from this middle glass than its focus, then it perceives the objects erect and 

 confused. 



Lastly, the third or immediate eye-glass adds nothing towards the erecting 

 or reversing the species, which it receives erect from the middle eye-glass; no 

 more than, in a telescope of two convex-glasses, the eye-glass adds to the 

 species it receives from the object-glass, as was shown before. The reason why 

 this last, or immediate eye-glass, has no concern in erecting or reversing the 

 species is the same, as in a telescope of two convex-glasses, viz. that the eye 

 is placed in its focus, and therefore sees the species as it is represented in the 

 distinct- base ; that is, the species is inverted in the distinct-base of the object- 

 glass, and therefore a single convex eye-glass brings it to the eye inverted ; but 

 in the distinct-base of the middle, or second eye-glass, the species is erect, and 

 therefore the third or immediate eye-glass brings it to the eye erect. 



Wherefore we are to consider the telescope, consisting of an object-glass 

 and three eye-glasses, as two telescopes, each consisting of two convex-glasses. 

 The first consists of the object-glass, and first eye-glass, and this inverts the 

 species ; that is, the species is inverted in the distinct-base of the object-glass, 

 and so brought to the eye. The second telescope consists of the two imme- 

 diate eye-glasses, and this erects what the former inverted, that is, the species 



