ORGANS OF THE SENSES THE EAR DIAGRAM 2 23 



becomes longer with. age. It is generally during tlie first years 

 of school that persons become short-sighted. To prevent this 

 as much as possible, children ought not to bring their eyes too 

 near their books and copy books ; they ought to read and write 

 holding the head straight, and at a little distance from their 

 desk. It is the master's duty to attend to this, and the number 

 of shortsighted children in his school will much depend on the 

 attention which he pays to the position of the children when 

 they work. 



Too short or too long sight is corrected by means of spectacles ; 

 but the selection of these is always a matter which requires much 

 attention, and anyone who supposes that he requires spectacles 

 ought always to consult the doctor before going to the optician. 

 The doctor, if he is skilful, will not only advise what spectacles 

 should be used, but in many cases will be able to give good ad- 

 vice to correct the sight, and render spectacles unnecessary for 

 the remainder of life. Tears are secreted by a gland placed in 

 the corner of the eye, outside and above, which is called the 

 lachrymal gland. 



Tfie ear. The ear hears the sounds produced by vibrating 

 bodies. It is always easy to ascertain by placing the hand on a 

 clock when it strikes, or on the cord of a musical instrument 

 while it is played, that bodies, when they produce a sound, 

 experience a kind of trembling or vibration which is very per- 

 ceptible to the fingers. We distinguish between the outer and 

 inner ear. The first, visible externally, is not indispensable to 

 hearing ; it is pierced with a hole called the auditory canal, which, 

 penetrates into the head, and communicates with the internal 

 ear. The bottom of the auditory canal is closed by a small 

 membrane stretched like the parchment of a drum, and called 

 the tympanum. It is therefore necessary to be always very 

 careful not to put hard bodies into the ^auditory canal as they 

 might break the tympanum, and cause serious accidents and 

 dreadful sufferings. 



Behind the tympanum are three very small bones of a singular 



