1 86 OF VERTIGO. Sect. XX. 7. 



one of his feet outwards, when he begins to incline, fuperadds 

 fear to his other inconveniencies ; which like furprife, joy, or 

 any great degree of fenfation, enervates him in a moment, by- 

 employing the whole fenforial power, and by thus breaking all 

 the afibciated trains and tribes of motion. 



7. The irritative ideas of objects, whilft we are awake, are 

 perpetually prefent to our fenfe of fight *, as we view the furni- 

 ture of our rooms, or the ground we tread upon, throughout the 

 whoie day without attending to it. And as our bodies are never 

 at perfect reft during our waking hours, thefe irritative ideas of 

 objects are attended perpetually with irritative ideas of their ap- 

 parent motions. The ideas of apparent motions are always ir- 

 ritative ideas, becaufe we never attend to them, whether we at- 

 tend to the objects themfelves, or to their real motions, or to 

 neither. Hence the ideas of the apparent motions of objects are 

 a complete circle of irritative ideas, which continue throughout 

 the day. 



Alfo during all our waking hours, there is a perpetual con- 

 fufed found of various bodies, as of the wind in our rooms, the 

 fire, diftant converfations, mechanic bufmefs ; this continued 

 buzz, as we are feldom quite motionlefs, changes its loudnefs 

 perpetually, like the found of a bell ; which rifes and falls as 

 long as it continues, and feems to pulfate on the ear. This any 

 one may experience by turning himfelf round near a waterfall ; 

 or by (Inking a glafs bell, and then moving the direction of its 

 mouth towards the ears, or from them, as long as its vibrations 

 continue. Hence this undulation of indiflinct found makes 

 another concomitant circle of irritative ideas, which continues 

 throughout the day. 



We hear this undulating found, when we are perfectly at reft 

 ourfelves, from other fonorous bodies befides bells ; as from two 

 crgan-pipes, which are nearly but not quite in unifon, when they 

 are founded together. When a bell is ftruck, the circular form 

 is changed into an elliptic one j the longeft axis of which, as the 

 vibrations continue, moves round the periphery of the bell ; and 

 when either axis of this ellipfe is pointed towards our ears, the 

 found is louder •, and lefs when the intermediate parts of the 

 ellipfe are oppofite to us. The vibrations of the two organ- 

 pipes may be compared to Nonius's rule ; the found is louder, 

 when they coincide, and lefs at the intermediate times. But, as 

 the found of bells is the moft familiar of thofe founds, \vhich 

 have a confiderable battement, the vertiginous patients, who at- 

 tend to the irritative circles of founds above described, generally 

 compare it to the noife of bells. 



The periftaltic motions of our ftomach and inteftines, and the 



fecretions 



