318 NATURAL HISTORY 



experiments, is the stone-built, tiled hop-kiln in Gaily 

 Lane, which measures in front forty feet, and from the 

 ground to the eaves twelve feet. The true centrum pho- 

 nicum, or just distance, is one particular spot in the 

 King's Field, in the path to Nore Hill, on the very 

 brink of the steep balk above the hollow cart-way. In 

 this case there is no choice of distance ; but the path, 

 by mere contingency, happens to be the lucky, the iden- 

 tical spot, because the ground rises or falls so immedi- 

 ately, if the speaker either retires or advances, that his 

 mouth would at once be above or below the object. 



We measured this polysyllabical echo with great 

 exactness, and found the distance to fall very short of 

 Dr. Plot's rule for distinct articulation : for the Doctor, 

 in his History of Oxfordshire, allows one hundred and 

 twenty feet for the return of each syllable distinctly: 

 hence this echo, which gives ten distinct syllables, 

 ought to measure four hundred yards, or one hundred 

 and twenty feet to each syllable ; whereas our distance 

 is only two hundred and fifty-eight yards, or near 

 seventy-five feet, to each syllable. Thus our measure 

 falls short of the Doctor's, as five to eight : but then it 

 must be acknowledged that this candid philosopher was 

 convinced afterwards, that some latitude must be ad- 

 mitted of in the distance of echoes according to time 

 and place 1 . 



When experiments of this sort are making it should 

 always be remembered that weather and the time of 

 day have a vast influence on an echo ; for a dull, heavy, 

 moist air deadens and clogs the sound ; and hot sun- 

 shine renders the air thin and weak, and deprives it of 

 all its springiness ; and a ruffling wind quite defeats the 

 whole. In a still, clear, dewy evening, the air is most 

 elastic ; and perhaps the later the hour the more so. 



1 It is evident too, from the previous statement of the different number 

 of syllables returned by the echo, according to whether they were quick 

 dactyls or heavy spondees, that some allowance must be made on this 

 account also. E. T. B. 



