OF HEARING. 175 



able motion in them, such as hares, cows, sheep, &c, the ear describes 

 a half conoid ; but the circumference of that cone is not a section of a 

 circle, but a side of an ellipse, with the long axis turned forward and 

 backward. Besides this conoid motion, the ears have a rotatory motion, 

 which attends the conoid ; so that, when the ear is turned forward, the 

 mouth of the funnel is likewise turned forward ; and when the ear takes 

 its sweep outward, the mouth of the funnel always corresponds to that 

 motion. All this order or division of animals has the membrana tym- 

 pani concave on its external surface ; and as all of this class are Tetra- 

 coilia, they have all a cochlea. 



Of Hearing. 



The hearing of animals is either acute, distinct, obtuse or obscure ; 

 fitted to the various ways of life. Some animals have only one of those 

 properties, while others have two or more. 



1st. The ' acute ' is for those animals, as mice, &c, that are a prey 

 to others, by which means they avoid danger. The acute is also for 

 those animals that prey upon others, as cats, &c, that they may the 

 better find their food. 



2nd. The ' distinct ' is where the animal can distinguish between one 

 sound and another, and take in the whole variety of sounds, such as the 

 human kind, many birds, some beasts. 



3rd. The 'obtuse' is for those animals that are not in danger of 

 being preyed upon, nor is it their way of life to prey upon others. 



4th. The 'obscure' is where animals cannot attend to, or are not 

 capable of taking in or distinguishing, the variety of sounds. This is 

 perhaps the largest class [or may characterize the majority of animals]. 



These four circumstances are the cause of such a variety of forms of 

 ears. 



The human kind, perhaps, possess the greatest share of any, espe- 

 cially of the second (quality), for they certainly can distinguish sounds 

 better than any other animals. ' 



The animals of the first class will require some degree of distinctness 

 as well as of acuteness : as by the particular sounds they will judge of 

 their proper food ; as, in the case of cats, the sound of mice or rats, the 

 fluttering of birds, &c. ; and so of other animals according to their 

 different kinds of food., The hearing of the third class will generally 

 be attended with obscurity and indistinctness ; for those animals, whose 

 way of life requires no great variety of action, which are in no great 

 danger themselves or endanger others, and which make no great variety 

 of sound themselves, will generally be attended with the fourth [quality 

 of hearing]. Animals will have distinctness in sound in proportion to 



