44* Echoes. [Book V, 



neceffary that the diftance Ihould be fuch, and the 

 reverberated or reflected found fo long in arriving, 

 that the ear may diftinguifh clearly between that and 

 the original found *. 



Reflected 



* " It is in general known, that caverns, grottoes, mountains, 

 and ruined buildings return this image of found. Image we may 

 call it, for in every refpeft it refembles the image of a vifible ob- 

 jeft reflected from a poliflied furface. Our figures are often re- 

 prefented in a mirror without feeing them ourfelves, while thofe 

 flanding on one fide are alone fenfible of the reflection. To be 

 capable of feeing the refle&ed image of ourfelves, we muft be di- 

 reUy in a line with the image. Juft fo is it in an echo ; we muft 

 ftand in the line in which the found is reflected, or the repetition 

 \v-ill be loft to us, while it may, at the fame time, be diftindlly 

 heard by others who itand at a fmall diftance to one fide of us. 

 I remember a very extraordinary echo, at a ruined fbrtrefs near 

 Louvain, in Flanders. If a perfon fung, he only heard his own 

 Voice, without any repetition ; on the contrary, thofe who flood at 

 Ibme diftance, heard the echo but not the voice ; but then they 

 heard it with furprifmg variations, fometimes louder, fometimes 

 fofter, now more near, then more dlftant. There is an account, 

 in the memoirs of the French academy, of a fimilar echo near 

 Rouen. The building which returns it is a femicircular court- 

 yard; yet all buildings of the fame form do not produce the fame 

 effects. We find fome mufic halls excellently adapted for founds, 

 while others, built upon the fame plan, in a different place, are 

 found to mix the tones, inftead of enlarging them, in a very dif- 

 agreeable manner. 



" As we know the diftance of places by the length of time a 

 found takes to travel from them, fo we may judge of the diftance 

 of an echo, by the length of the interval between our voice and 

 its repetition. The moft deliberate echoes, as they are called, 

 are ever the moft diftant; while, on the contrary, thofe that are 

 very near, return their founds fo very quick as to have the inter- 

 val almoft imperceptible ; when this i.s the cafe, and the echo is 

 fo very near, the voice is faid to be increafed and not echoed ; 

 however, in faft, the increafe is only made by the fwiftly purfuing 

 repetition. Our theatres and concert rooms are beft fitted for mu- 

 fic or fpeajcing, when they enlarge the found to the greateft pitch 

 at the fmalleft interval : for a repetition which does not begin the 



word 





