[488] 
The third Probleme is. That a Sound may he con* 
veyd from one extreme to the other ( or from one di- 
ftant place to another J So as not to be heard in the 
middle. 
By the help of this Probleme a man may talk to 
his freind at a very confiderable diftance, fo that 
thofe in the middle fpace fliall hear nothing ot what 
pa fled betwixt them. 
Fig. 2. 
Semiplanum Sph^zr^x ?honic<z feu Acou/iic<^. 
You are tp conceive that (rude) Semiplane^ as Paral- 
lel to the Horio^pn. For if it be Perpendicular thereunto, 
I fuppofe the upper extremity will be no^nger Circular^ 
but Hyperbolical, and the lower part oi it fuited to a 
greater Circle of the Earth. So that the whole Phom* 
cal Sphear f if I may fo call it ) will be a Solid Hyperbo- 
A?, ftanding upon 2i Concave Sphterical Bafe. I fpeak 
this concerning Sounds made ( as ufually they are ) nigh 
the Earth, and whole Sonorous medium has a free paflage 
every way. For if they are generated high in the Air, 
ordiredled one way, the cale will be different ; which is 
partly defigndin the inequality of that draught. 
Cer- 
