i8 4 OF VERTIGO. SECT. XX. 6. 



azine on the apparent retrogreffion of obje&s in vertigo, I am 

 induced to believe, that this apparent retrogreffion of objects is 

 not always owing to the fame caufe. 



When a perfon revolves with his eyes clofed, till he becomes 

 vertiginous, and then (lands (till, without opening them, he feems 

 for a while to go forward in the fame direction. This halluci- 

 nation of his ideas cannot be owing to ocular fpt-ftra, bec^ufe, 

 as Dr. Wells obferves, no fuch can have been formed ; but it 

 muft arife from a fimilar continuance or repetition of ideas be- 

 longing to the fenfe of touch, initead of to the fenfe of vifion j 

 and (hould therefore be called a tangible, not a vifual, vertigo. 

 In common language this belief of continuing to revolve for 

 fome time, after he (lands ftill, when a perfon has turned round 

 for a minute in the dark, would be called a deception of imagin- 

 ation. 



Now at this time if he opens his eyes upon a gilt book, placed 

 with other books on a (helf about the height of his eye, the gilt 

 book feems to recede in the contrary direction j though his eyes 

 are at this time kept quite ftill, as well as the gilt book. For 

 if his eyes were not kept ftill, other books would fall on them in 

 fucceflion , which when I repeatedly made the experiment, did 

 not occur ; and which thus evinces, that no motion of the eyes 

 is the caufe of the apparent rerroceffion of the gilt book. Why 

 then does it happen ? Certainly from an hallucination of ideas, 

 or in common language the deception of imagination. 



The vertiginous perfon flill imagines that he continues to re- 

 volve forwards, after he has opened his eyes , and in confe- 

 quence that the objects, which his eyes happen to fall upon, are 

 revolving backward , as they would appear to do, if he was ac- 

 tually turning round with his eyes open. For he has been ac- 

 cuftomed to obferve the motions of bodies, whether apparent or 

 real, fo much more frequently by the eye than by the touch ; that 

 the pretent belief of his gyration, occafioned by the hallucina- 

 tions of the fenfe of touch, is attended with ideas of fuch imag- 

 ined motions of vifible objefts, as have always accompanied his 

 former gyrations, and have thus been aflbciated with the mufcu- 

 lar actions and perceptions of touch, which occurred at the 

 fame time. 



When the remains of colours are feen in the eye, they are 

 termed occular fpe6tra ; when remaining founds are heard in 

 the ear, they may be called auricular murmurs ; but when the re- 

 maining motions, or ideas, of the ienfe of touch continue, as in 

 this vertigo of a blind-folded perfon, they have acquired no name, 

 but may be termed evanefcent titillations, or tangible hallucina- 

 tions. 



Whence 



