OF HEARING. 171 



of the refracting power (which might be supposed to be a cause), nor 

 an alteration in the form of the refracting power (either of which would 

 oblige the focal point or whole shape of the eye to vary) ; but it is a 

 defect in adapting the eye to near objects ; for all such do not see 

 distant objects better than formerly, but they do not see near objects 

 so well as formerly. 



The circumstance takes place in those only who have been used to 

 see well objects both near and at a distance, and they lose the near 

 sight ; whereas those who only saw well objects that were near, have 

 the natural focal point near, and continue to see them at that distance. 

 But it must be remembered that they never had a great scope of focal 

 action in the eye, or else they would have adapted it to more distant 

 objects. 



Every eye has a natural focal point, viz. that point which requires no 

 exertion of the eye to adapt itself to it ; whereas every object within, 

 or beyond [the natural focal point], requires an exertion of the eye to 

 adapt its focus to that object; and, the further [the object may be] 

 from the natural focal point, either way, the greater the action required. 



Of the Organ of Hearing. 



The organ of hearing is peculiar to certain classes of animals ; the 

 more imperfect do not appear to be endowed with this sense. Insects 

 certainly have it, if what is related of bees be true : however, I have 

 not been able to discover the organ itself below fish 1 , where it is very 

 conspicuous. 



It is a specific or peculiar organ for the sensation of sounds, the 

 organ itself answering no other known purpose, which is not the case 

 with the nose and tongue. 



As the matter, or body, which is the first cause of sound, is not in 

 contact with the organ, there must be an intermediate connexion or 

 medium between the two. This medium is not confined to any one 

 species of matter, which circumstance we may suppose produces a 

 variety, and therefore the organ must vary in some degree according to 

 the medium. The air appears to be the proper medium for us, but 

 water is the medium for fish : however, even to us the medium is not 

 confined to air, nor can we justly suppose that it is confined to water in 

 fish. 



1 [In the year 1782, Hunter stated, in his account of the Organ of Hearing in 

 Fish, read before the Royal Society, " that the class called Sepia has this organ also, 

 but somewhat differently constructed from what it is in the Fish." — Phil. Trans. 

 1782, p. 380.] 



