DULATORY FORCES ACOUSTICS. 



[TITR 



it protected from the intrusion of intecti and foreign 

 rnMt-r, by means of haira, and a peculiar wax-like *e- 

 xeeM. often becomes hardened, and 

 in tbiu the eane of difficulty of hearing, which tome 

 panoM mffar frm. It it, however, readily removed by 

 syringing the ear with warm water. The following cut 

 will give an idea of tlw different parts of the human 



ear. 



. Ji. 



The orpins of hearing in the lower animals are all 

 constructs! on similar principles to those <>f the human 

 lified. however, no as to meet the special cir- 

 ancos of the individual. 



Amongst the mammalia, we find the ear, generally 

 peaking, defended externally by a large flap, which 

 nerve* to protect it from being injured by inserts ,.r tin- 

 twig* of tree*, as the animal passes through a thicket : 

 this may be best noticed in the elephant and 

 the dog. AH animals of prey nro possessed of 

 great lowers of hearing, on which they partly 

 nd fT success in the search for food. Am- 

 phibious animals can readily adapt their organs of 

 hearing to the medium in which they may for the 

 moment dwell. Without such a provision, these 

 animals would sustain much inconvenience, and 

 suffer extreme pain, when beneath the surface of 

 water. This is chiefly owing to the great con- 

 ducting power of that liquid, by which Bounds 

 ;ict more strongly on the tympanum than when 

 conveyed by air ; and if the organ were 

 tected, under such circumstances, it^ 

 ness would speedily be destroyed. Tim <-nr* 

 of birds are not easily distinguished externally, 

 owing to the outer ori6ce being covered with 

 feathers. As we descend in the scale of nature, 

 we find that these organs become of simpler con- 

 struction ; and, passing by fishes, we at last 

 lin.l their development to be but rudimentary in 

 the tribe of insects. On this subject, wo refer 

 our readers to the excellent remarks of J)r. 

 Bushnan, which will be found at page 3C in 

 the second volume, in the section of Comparative 

 Physiology. 



m. l lk<- tm\ t>T wMrh nmt<1 Touch tt\* drum, k; r ! (V Hnntni-Vrm tiihi- ; 

 t uut r rrpn-wnt the conun-n<Mn. <>[ tin- .u.-l i.iy mtv- n witli llie IHMMI ; 

 / >n.| g an U up|r and lower portioiu of the eilerual flohy part of 



COKCLUDING REMARKS ON THE T7NDULATORY FORCES. 



W have now completed our exposition of the laws of those forces which, although, so far as wo at present know, 

 have not that extensive application possessed by gravitation and cohesion, are yet only second to them in that respect. 

 As we proceed, the student will observe how large is their range ; and more particularly, in the next section, will he 

 notice their inijiortanco in the general economy of nature. Their consideration, in fact, forms a fitting am'. 

 introduction to the study of chemistry, on the limits of which we have ofteu had to tread. All the operations in tho 

 laboratory of nature, as in that of tiio chemist, depend on the exertion of one or more of the forces we have so 

 treated on ; and it will therefore be desirable that our readers shall have become well acquainted with 

 the principles already expounded, before they attempt to make farther progress. 



In tho sections on Applied Mechanics and Meteorology, we shall have frequently to refer to what has already 

 been enunciated. This aifords an additional reason for the remarks we here make, and points out to the student tho 

 uccuwity of a close investigation of each of the preceding sections, its a preparation for such as are to follow. 



