ofOXFo%$>~SHl%E. 9 



Geometrical paces, or 120 feet, I guefs'd that the object could 

 not be removed lefs than 400 of the former, and 2000 of the 

 latter. For the better undetftanding of which Analyfis, and for 

 the Readers more fecure finding of the true diftance of the 

 fpeaker in any other place, it may be convenient that he take no- 

 tice, that all Echo's have fome one place whither they are return- 

 ed ftronger, arid more diftindt than any other, and is always the 

 place that lies at right angles with the object, and is not too near,' 

 Of too far off": for if a man ftand at oblique angles with it, the 

 voice is better returned to fome other perfon at another place 1 , 

 than to the fpeaker ; andfo if he ftand too near, or far off, aU 

 though he do ftand at right angles with it, which is plain by the 

 diagram, Tab. i.Fig. 3. where 



a. is the true place of the fteaker. 



a b. the vocal line falling at right angles on the objeft. 



cd. places on each hand the true place, and oblique to the object. 



e f. places above and below the objecl, whence atfo the voice 



comes obliquely to it, 

 g h. places whence (?tis true) the voice goes in right Angles to 



the objett, but g is too far off, and h too near* 



Now the fpeaker ftanding in 4* and his voice going in the ftraight 

 line a b, and ftriking upon the object fo as to make right angles 

 with it, muft needs return to the fpeaker again in the fame line* 

 and no farther, becaufe he is fuppos'd to ftand at the two ex- 

 treams of the whole mix'd line of action i but if he ftand too 

 near at h, then the Echo repeat's mote fyllables, anddiftinfter at 

 g than either at h or a, becaufe g is now the extream of the line 

 0^ action ; for by how much the nearer the fpeaker is to the ob- 

 ject, by fo much the more forcible he ftrikes it, which caufes the 

 rebound to be fo much beyond him : and thus if he ftand as much 

 too far off, asatg, then the Echo repeats more fyllables and di- 

 ftinfter at h, then either at a or g, becaufe the diftance being too 

 great from g to b, and the reflexion weak, the Echo muft needs 

 terminate fo much the (horterat^5 allthefe being fuppofed to 

 take up the whole line of the voices direct and reflex action, A- 

 gain, if the fpeaker ftand in c obliquely to the object, the Echo h 

 better heard at */, than either at a or c ; andfo if he fta"nd at d t 

 it is better heard ate then any other place : thus if he ftand at e 



B above* 



