*So OF VERTIGO. SECT. XX. ft. 



irritative motions, and of 'the aflbciate motions 

 catenated with them. 



Many people, when they arrive at fifty or fixty 

 years of age, are affected with flight vertigo; 

 which is generally but wrongly afcribed to indigef- 

 tion, but in reality arifes from a beginning defect 

 of their fight ; as about this time they alfo find it 

 neceifary to begin to ufe fpectacles* when they read 

 fmall prints, efpecially in winter^ or by candle light, 

 but are yet able to read without them during the 

 fummer days, when the light is ftronger. Ihefe 

 people do not fee objects fo diftinctly as formerly j 

 and by exerting their eyes more than ufual, they 

 perceive the apparent motions of objects, and con* 

 found them with the real motions of them $ and 

 therefore cannot accurately balance themfelves fo 

 as eafily to preferve their perpendicularity by 

 them. 



That is, the apparent motions of objects, which 

 are at reft, as we move by them, mould only excite 

 irritative ideas : but as thefe are now become lefs 

 diftirict, owing to the beginning imperfection of 

 our fight, we are induced voluntarily to attend ta 

 them ; and then thefe appaient motions become 

 fucceeded by fenfation ; and thus the other parts of 

 the trains of irritative ideas, or irritative mufcular 

 motions, become difordered, as explained above. 

 In thefe cafes of flight vertigo I have always pro- 

 mifed my patients, that they would get free from it 

 in two or three months, as they mould acquire the 

 habit of balancing their bodies by lefs diftinct ob- 

 jects, and have feldom been miftaken in my prog- 

 noftic. 



There is an auditofy vertigo, which is called a 

 noife in the head, explained in No. *;. of this fecti- 

 on, which alfo is very liable to affect people in the 

 advance of life, and is owing to their hearing lefs 

 perfectly than before. This is fometimes called a 

 * ringing 



