Microscopical Essays. ^ 



6. That every ray of light carries with it the image of the 

 object from which it was emitted. 



The nature of virion in the eye, may be imperfectly illuftrated 

 by the experiment of the darkened room ; the pupil of the eye 

 being confidered as the hole through which the rays of light pafs, 

 and crofs each other, to paint on the retina, at the bottom of the 

 eye, the inverted images of all thofe objects which are expofed to 

 the fight, fo that the diameter of the images of the fame object 

 are greater, in proportion to the angles formed at the pupil, by 

 the croffing rays which proceed from the extremities of the ob- 

 ject; ; that is, the diameter of the image is greater, in proportion 

 as the diftance is lefs ; or, in other words, the apparent magni- 

 tude of an object is in fome' degree meafured by the angle under 

 which it is feen, and this angle increafes or diminifhes, according 

 as the object is nearer to, or further from the eye ; and confe- 

 quently, the lefs the diftance is between the eye and the object,, 

 the larger the latter will appear. 



From hence it follows, that the apparent diameter of an object: 

 feen by the naked eye, may be magnified in any proportion we 

 pleafe ; for as the apparent diameter is inereafed, in proportion 

 as the diftance from the eye is leffened, we have only to lefien 

 the diftance of the object from the eye, in order to increafe the 

 apparent diameter thereof. * Thus, fuppofe there is an object, 

 AB, Plate I. Fig. i, which to an eye at E fub tends or appears 

 under the angle AEB, we may magnify the apparent diameter 

 in what proportion we pleafe, by bringing our eye nearer to it. 

 If, for inftance, we would magnify it in the proportion of FG 



tO) 



* Rutherfortk's Syftem of Natural Philofophy, p. 330. 



