SECT. XX. i. OF VERTIGO. 175 



SECT. XX. 



OF VERTIGO. 



I . We determine our perpendicularity by the apparent motions of ob- 

 jecls. A perfon hood-winked cannot walk in a Jlraight line. 

 Dizzinefs on looking from a tower , in a room gained with uni- 

 form lozenges > on riding overfnow. 2. Dizzinefs from moving 

 objecls. A whirling wheel. Fluctuations of a river. Experi- 

 ment with a child. 3. Dizzinefs from our own motions and 

 thofe of other objecls. Riding over a broad ftream. Sea-ftcknefs. 

 5 Of turning round on one foot. Dervifes in Turkey. Atten- 

 tion of the mind prevents flight fea-Jickneft. After a voyage ideas 

 cf 'vibratory motions are ftill perceived onfhore. 6. Ideas con- 

 tinue feme time after they are excited. Gircumjiances of turning 

 on one foot iflanding on a tower ^ and walking in the dark> explain- 

 ed. 7. Irritative ideas of apparent motions. Irritative ideas of 

 founds. Battemens of the found of bells and organ-pipes. Ver- 

 tiginous noife in the head. Irritative motions of thejiomach, in- 

 teJiineS) and glands. 8 Symptoms that accompany vertige. Why 

 vomiting comes on in Jirokes of the palfy By the motion of ajhip. 

 By injuries on the head. Why motion makes ftck people vomit. 

 9. Why drunken people are vertiginous. Why a Jione in the ure- 

 ter ', or bile-duel^ produces vomiting. i o. Why after a voyage 

 ideas of vibratory motions are perceived on Jhore* II. Kinds of 

 vertigo and their cure. 12. Definition of vertigo. 



i. IN learning to walk we judge of the diftancesof the ob- 

 jefts, which we approach, by the eye ; and by obferving their 

 perpendicularity determine our own. This circumftance not 

 having been attended to by the writers on vifion, the difeafe 

 called vertigo or dizzinefs has been little underftood. 



When any perfon lofes the power of mufcular aclion, wheth- 

 er he is ereft or in a fitting pofture, he finks down upon the 

 ground ; as is feen in fainting fits, and other inftances of great 

 debility. Hence it follows, that fome exertion of mufcular pow- 

 er is neceflary to preferve our perpendicular attitude. This is 

 performed proportionally exerting the antagonilt mufcles of the 

 trunk, neck, and limbs ; and if at any time in our locomotions 

 we find ourfelves inclining to one fide, we either reftore our 

 equilibrium by the efforts of the mufcles on the other fide, or 

 by moving one of our feet extend the bafe, which we reft upon, 

 to the new centre of gravity. 



But the moft eafy and habitual manner of determining our 



want 



