Mifiellanea Curiofa. 1 3 5 



III. fyfleBed Vifion has been improvM by the 

 Invention of hookjng-glaffes and Polifod Metals, 

 whether Plane, - Concave, or Convex ; and thefe 

 two laft:, either Spherical, Oval, Cylindrical, Co- 

 nical, Hyperbolical, or of feveral other (hapes ; all 

 which caufe a different Reflection, and vaty the 

 Phenomena, 



Thus alfo Bsflext Audition, made by Ecchoes, 

 may be improv'd, by contriving Jeveral forts of 

 Artificial Ecchoes j as 'tis no hard matter to do in 

 almoft any place. 



For (fpeaking in the general) Any Sound, fall* 

 ing direHly or cbliauely upon any denfe Body, of a 

 finooth (whether Plane or Arched) Superficies, is beat 

 bacl^again and refiefled, or does eccho more or lefs. 



I fay (i.) falling diretlly or obliquely ; becau/e, 

 if the Sound be fent out and propagated parallel 

 to the Surface of the Denfe Body, or be made fb 

 far offend fb weak.* that it cannot reach it, there 

 will be no Reflection of Sound,no E echo. 



I fay (z.) upon a Body of a frnoo'h Superfi- 

 cies ; becaufe if the Surface of the Corpus Ob~ 

 pans be uneven, the Air by reverberation will 

 be put out of its regular Motion, and the Sound 

 thereby broken and extinguiuYd : So that tho' 

 in this cafe alfb the Air be beaten back again, 

 yet Sound is not reflected, nor is there any 

 Eccho. 



I fay (3.) it does eccho more or lefs, to fhew, 

 that when all things are, as is before defcrib'd, 

 there is ftill an Ecchoing, though it be not al- 

 ways heard ; either becaufe the diretl Sound is 

 too weak to be beaten quite back again to him 

 that made it ; or that it does return home to 

 him, but fo weak, that without the help of a 

 goodXitacouftick. it cannot be difcern'd j or that 

 K 4 he 



