293 



But, let r s, r ty reprefent two other rays falling upon the —than a pencil 

 lens in an oblique direftion; thefe rays after paffing ^'^''ough from thc^center. 

 the lenvS, will both be refrafted towards the left hand, and will 

 therefore have *' a mutual inclination" to each other when they 

 fall upon the eye at y, turned to view an object in the direc- 

 tion ry ; hence an object viewed in that direflion, wrill be 

 feen more diflindly, than if it were viewed through the centre 

 of the lens. 



The fame thing may be proved experimentally, thus; let a Experiment 

 perfon when reading with fpeflacles that are proper for his ^f^^^^^r '"/"P" 

 fight, look attentively for a moment, at a lingle word through doftrine. 

 the centres of his glaflfes. Then let him turn his head, either 

 to the right or to the left, (without moving the book) fo that 

 the fame word may be feen by oblique rays, and it will appear 

 much more diftin6lly than before. 



From what has been advanced it appears, that when glafTes Inference : 

 are put into frames for fpeaacles, thofe glafles Ihould ftand in ^a^^e/^^ou'^hf to 

 an oblique direction, that the rays of light ifluing from ^n ob- be fixed ob- 



jea,*^^^«'y» 



