48 NATURAL THEOLOGY. 



ther ; and, by the result of their action, work the 

 base of that which is the last in the series, upon 

 an aperture which it closes, and upon which it 

 plays, and which aperture opens into the tortuous 

 canals that lead to the brain. This last bone of 

 the four is called the staj^es. The office of the 

 drum of the ear is to spread out an extended sur- 

 face, capable of receiving the impressions of sound, 

 and of being put by them into a state of vibration. 

 The office of the stapes is to repeat these vibra- 

 tions. It is a repeating frigate, stationed more 

 within the line. From which account of its action 

 may be understood how the sensation of sound 

 will be excited by any thing which communicates 

 a vibratory motion to the stapes, though not, as in 

 all ordinary cases, through the intervention of the 

 membrana tympani. This is done by solid bodies 

 applied to the bones of the skull, as by a mental 

 bar h olden at one end between the teeth, and 

 touching at the other end a tremulous body. It 

 likewise appears to be done, in a considerable de- 

 gree, by the air itself, even when this membrane, 

 the drum of the ear, is greatly damaged. Either 

 in the natural or preternatural state of the organ, 

 the use of the chain of bones is to propagate the 

 impulse in a direction towards the brain, and to 

 propagate it with the advantage of a lever ; which 

 advantage consists in increasing the force and 

 strength of the vibration, and at the same time 

 diminishing the space through which it oscillates ; 



