I2if OBSERVATIONS ON VENTRILOQUISM. 



pulfes which fall upon them : therefore, as often as the two 

 portions of the head, which are feparated by the vertical 

 plane perpendicular to the axis of hearing, are equally agi- 

 tated by the pulfes of the fame found, the ears are alfo equally 

 aflfe&ed from the fame caufe ; which never happens, as vvc 

 learn from the teftimony of the other fenfes, unleft the found- 

 ing body be placed fomewhere in the right line that bife&s the 

 axis of hearing at right angles. In this manner men are taught 

 by experience to draw a general inference from a general ob- 

 servation ; they therefore conclude a body to be fituated di- 

 rectly before or behind their perfons, as often as the found of 

 it ftrikes both their ears with equal forces. 

 Phenomena of The phenomena of oblique hearing remain to be explained ; 

 oblique heanng. vv hj c h ca f e occurs as often as the founding body is fituated in 

 the horizontal plane, but not in the right line that bifecls the 

 axis of hearing at right angles. Let M be the place of the 

 founding body, and draw M O to the centre of the circle ; 

 alfo let O C bifeft the arc ECF, and take O G i. it equal to 

 O M : alfo draw W M, M R, P G, G I tangents to the 

 circle. Now fuppofe a found equal to that at M, to proceed 

 from G, then the latter would have the fame effect on the arc 

 TCP that the former has onWDR, becaufe the arcs are 

 manifeftly equal, and alike fituated relative to the points M 

 and G. But the found proceeding from G is a cafe of direct 

 hearing, confequently the ears placed at E and F receive 

 equal impreffions from it, which is not the cafe with the 

 pulfes that flow from M. For though the forces imparted to 

 the two arcs, TCP, W D R are equal, they do not fall 

 equally on the circle in refpecl: to the points E and F, which 

 reprefent the ears; the found therefore coming from M ftrikes 

 tlie'fe organs with unequal forces, as may be eafily inferred 

 from the figure, 

 pra&ical delica- The judgment of the direction of founds by Mr. Gough's 

 cy of perception ear was p Ce cife to about eight degrees of pofition as to the 

 of found. horizon, and about ten degrees as to elevation above its plane. 



Peception of The faculty by which men judge of the dire&ion of founds 



hearing from mu ft inevitably be liable to deception, whenever the fonorife- 

 rous undulations are made to arrive in a direction which is not 

 from the fonorous obje6t, as in the cafe of echo ; and thefe 

 deceptions will be the more ftriking, as we are apt to rely on 

 the teftimony of the fenfe with the moft implicit confidence. 



Upon 



