24-8 ON VENTRILOQUISM. 



ftronger, and proceeded from the tray. The certainty of the 

 latter circumftance was afcertained by changing the place of 

 the reflector, fo as to make the found fall upon my right and 

 left ears alternately. 

 Eiq>- a. A fmall Exp, 2. The refult of the laft experiment convinced me 

 metallic rattle f ^ e practicability of turning the echos of a room to the ufe 

 inftead of the °f a ventriloquift, feeing I had employed thofe of my own 

 watch ; and ] a p to a fimilar purpofe ; neverthelefs I defired to give an 

 tried: with additional proof of the fame thing, by the afiiftance of a 

 fimilar iefults. ftronger found. With this view, I took a fmall metal rattle, 

 belonging to a child's toy ; it weighed 25 grains, and con- 

 fided of two thin convex (hells of brafs, fomething lef? than 

 one inch broad: a pellet was lodged in the cavity formed by 

 the junction of thefe hollow plates; the motion of which pro- 

 duced a found, fuch as I wanted. This rattle being put into 

 the fame-cocoa nut prepared as in the laft experiment, I gave 

 a gentle motion to it by my finger, which was introduced at 

 the aperture ; and I foon perceived, that the found might be 

 transferred in this cafe alfo, from the fhell to the tray, but 

 not with equal certainty : for frequently a flight change, given 

 to the inclination of the refleclor, rendered the place of the 

 found evident, which was indiftinci before ; and the contrary. 

 The reafon of this uncertainty will be inveftigated hereafter; 

 and I may add at prefent, that a thin quarto as well as a fan 

 were fubftituted with fuccefs, in lieu of the tray; but bodies 

 of three or four inches in diameter, did not produce the effect. 

 The preceding experiments have been related with an atten- 

 tion to circum (lances, which cannot fail of inftru&ing any 

 one to repeat them accurately ; and a few trials will, without 

 doubt, convince him who will take the trouble, that the echos 

 of a room are fubjecl to external influence, as well as thofe of 

 a valley. 

 Obfervations on We come in the next place to examine the peculiarities 

 the fads. The that gave rife to thefe counterfeit founds ; that is the unufual 



ieflec~ted found c j rcum ft a nces f m y experiments are to be reviewed, and 

 was made to pre- j r . 



dominateover, their effects afcertained. The (hell was enconi nailed by a bad 



and obliterate the conr ] u fl or f found on all fides, the mouth excepted; it was 

 direcUound, &c. . * 



from this aperture then, that the pulles entered theatmolphere 



with their wonted freedom. Now we know from experience, 



that confined found does not diverge from the place of its 



egrefs, as it. were from a centre : for fliould any one attend to 



a 



