Of 0XF01{'D^SHI'i{E. ij 
rather than others ; juft as in two Viols tuned to zVnifon^ where 
the firings being fcrewed to the fame tenfion, and their pores 
put into the fame figure, if you ftrike one, the correfponding 
firing of the other Viol prefently anfwers it : becaufe the firft 
firing being of fuch a tenfion, and having pores of fuch a form, 
makes vibrations in the Air, fuitable only to the pores made by 
the fame tenfion in the other firing. 
2$. As for Tautological Polyfhonom Echo's^, fuch as return a 
word or more, often repeated from divers objefts by fimple re- 
flexion, there are none here ejiiinent ; the beil I have met with 
isztEwelme^ on the fide of a bank, inaMeddow fouth and by 
wefl (about a furlong) from the Church : it returns the fame word 
three times, from three feveralobjeds of divers diflances, which 
I guefs may be, i. The Ma nor ^ 2. The Church znd HoPpital^ 
And 'f. Colonel Martins houfe. Another there is near Oxford^ a- 
bont the eafl-end of Chrift Church new walk, that repeats three or 
four fyllables twice over ; and a treble one at the mofl northern 
point of the Fortifications in New Parks : But there being many 
better than thefe of the kind no doubt in other places, I (ball ree- 
fer ve their confideration at large to a better opportunity, and on-^ 
ly take notice here by the way , that thefe are never of many fyl- 
lables ; and that always, by how many more they are of, by fo 
many the fewer times they repeat them, becaufe fo great diflance 
will be required for their objects, that they mufl quickly be re- 
moved out of the reflex aftion of the voice : for fuppofe but a 
fentence of ten fyllables, viz^ Gemitu nemm cmne remugit^ and 
allow, as before, for the return of each fyllable 1 20 feet, the firfl 
objed mufl be 1 200 feet ofl'; and the fecond, vi^ith abatement for 
diflance, at leafl 2000 ; and the third, certainly out of the 
voices reach, beyond all hopes of any rcfponfe. Indeed, could 
we meet with one of M(irfennws\ Echo''s^ where fixty nine feet 
would return us a fyllable, thenTuch an Hemiftick. might be re-- 
founded three times, or perhaps a whole Heocanieter twice ; yet 
however fmalla fpace may be found for the clear repetition of 
fuch aVerfe, I cannot think it can pofTibly be, that any Echo 
fliould repeat one eight times over : for fuppofe a fmaller diflance 
would futtice, then that allowed by Merfcnnus^ as but 350 yards 
to a Verfe of feventeen fyllables, and allowing fome decreafe 
for the objects diflances; yet I do not doubtj, but two or 
three 
