Eyes and other Objects. 63 



exposed. But before you look at their appearance 

 when magnified, shall we pause for a few minutes to 

 inquire what place the white ball occupied in the 

 economy of the fish's eye ? and what was the jelly- 

 like mass which surrounded it ? Both may well occupy 

 our attention, as having united to form that most beau- 

 tiful piece of mechanism, an eye. The jelly-like mass 

 is the dismantled frame-work of an exquisite minia- 

 ture camera-obscura, of which the little white sphere 

 (transparent till boiling rendered its outside portion 

 opaque) was the lens : for the eyes of fishes, as well 

 as our own eyes, and those of all the other verte- 

 brated animals, are constructed on a plan exceedingly 

 similar to that of the camera-obscura. Its plan is not 

 difficult of comprehension; here I speak not of its 

 portentous form as a photographic engine, but when it 

 is literally a dark room for the exhibition of a land- 

 scape. It was first described so long ago as 1589, by 

 a Neapolitan philosopher, Gianbattista Porta; his 

 first plan was a simple dark room, with a closely fas- 

 tened shutter, in which a small hole should be made, 

 and the light permitted to fall on a white screen or 

 wall ; for he found that an image of the outside view 

 would be thus obtained. And that this effect would 

 follow, we can easily show, by holding a card pierced 

 with a round hole near a lighted candle, when we shall 

 see an image of the candle flickering on the wall, in 

 the card's shadow. But Porta bethought him of a 

 great improvement in his dark room contrivance, and 

 states it as a secret, which he had long concealed, and 

 had at one time intended always to conceal, that if a 



