ON VENTRILOQUISM. 24<9 



a noife coming from an open window, he always finds it 

 ftrongeft, in front of the paflage ; founds therefore refemble 

 the properties of a river entering a lake ; the current of 

 which affects its former direction, after it is freed from the re- 

 ftraints of a channel. My ear was placed behind the ap- 

 paratus, in relation to the (hell's mouth ; confequently it did 

 not lay in the track of the direct pulfes ; therefore the found, 

 heard by me in the abfence of the reflector, (hall be fuppofed 

 at prefent to have confuted wholly of lateral pulfes, reflected 

 from the circumference of the aperture ; but when a greater 

 mafs of found was forced on the ear, from a different quar- 

 ter, the weaker became imperceptible; which is a thiiig, 

 that happens invariably in fimilar cafes; this change in the 

 direction of the prevailing pulfes neceffarily transferred the 

 feat of the found from the fhell to the reflector. But if the re- The fame effeft 

 fleeted lateral pulfes can be filenced in one cafe, by diverting^ y produciblc- 

 thofe of the centre towards the fame parts ; a like rule might 

 be expected to obtain in all cafes: becaufe the powers of re- 

 flected founds may be fuppofed to have a fixed relation to thei r 

 primitives ; but the rule fails in a number of inftances ; con- 

 fequently my artificial ventriloquift pofleiTes another fource of 

 found ; which is the next fubject of inquiry. 



Exp. 3. When I let the fmall rattle tall from the height of E *P; 3- The 

 . i i if i • i i- i i n m i n i rattle was let fall 



an inch, upon the cloth which lined the tnell the liroke wasj n ; ts confining 



heard in the nut ; but the noife, occafioned by the rebounding receptacle. The 

 of the pellet, came from the reflector; in this inflance then, ce tac j e gave a " 

 we have two founds, proceeding from different places, though di eel found ; 

 they evidently iflued from the fame fpot ; and the caufe, that re £ r * nd "a Ve t he 

 gave them oppofite directions, may be investigated in the reflex found t 

 following manner. The ftroke of the rattle gave vibrations 

 to the fhell, which were ftronger than thofe imparted by the 

 pellet ; the former fet of vibrations could not be fuppreffed by 

 the pillow on account of their firength, they therefore pro- 

 duced a found, conjointly with the lateral pulfes, which proved 

 an overmatch for the echo of the reflector ; while the feebler 

 force of the fecond fet was overpowered by the pulfes, reflect- 

 ed from the tray. In reality the art of fupprelling the direct The fecret of 

 found appears to conftitute the fecret of ventnloquifm ; foj^^jj^ 

 the more completely this found is fmothered, the eaiier it is todirect found. 

 place the reflector properly : this appears to be the reafon, 

 why the experiment fucceeds with a watch more frequently 



than 



