226 
NATURAL HISTORY 
The true objed of this echo, as we found by various experi- 
ments, is the ftone-built, tiled hop-kiln in Gally-lane, which mea- 
fures in front 40 feet, and from the ground to the eaves 12 feet. 
The true centrum pkonkum, or juft diftance, is one particular fpot 
in the King's -field, in the path to Nore-hill, on the very brink of jhe 
fteep balk above the hollow cart way. In this cafe there is no 
choice of diftance ; but the path, by meer contingency, happens to 
be the lucky, the identical fpot, becaufe the ground rifes or falls 
fo immediately, if the fpeaker either retires or advances, that his 
mouth would at once be above or below the objeft. 
We meafured this polyfyllabical echo with great exadnefs, and 
found the diftance to fall very ftiort of Dr. P/o/'s rule for diftind: 
articulation ; for the Doiftor, in his hiftory of Oxford/jyire, allows 
120 feet for the return of each fyllable diftinftly : hence this echo, 
which gives ten diftinft fyllables, ought to meafure 400 yards, or 
120 feet to each fyllable; whereas our diftance is only 258 yards, 
or near 75 feet, to each fyllable. Thus our meafure falls fliort 
of the Doftor's, as five to eight : but then It muft be acknowledged 
that this candid philofopher was convinced afterwards, that fome 
latitude muft be admitted of in the diftance of echoes according to 
time and place. 
When experiments of this fort are making, it fliould always be 
remembered that weather and the time of day have a vaft in- 
fluence on an echo ; for a dull, heavy, moift air deadens and 
clogs the found ; and hot funfliine renders the air thin and weak, 
and deprives it of all it's fpringinefs ; and a rufRing wind quite 
defeats the whole. In a ftill, clear, dewy evening the air is moft 
elaftic ; and perhaps the later the hour the more fo. 
Echo 
