4 
Dr. Wollaston on the Duration 
wood with a regular motion along the notches, I could imitate 
pretty correctly the tremor produced by the pressure of my 
thumb against my head, and by marks to indicate the number 
of notches passed over in 5 or 10 seconds, observed by my 
watch, I found repeated observations agree with each other 
as nearly as could be expected ; for I could not depend upon 
exerting the same degree of force in different trials. 
That I might not be deceived by the resemblance of tre- 
mors, which coincided only at alternate beats, and therefore 
might be considered as octaves in music to each other, I some- 
times employed notches at greater and sometimes at less dis- 
tances from each other, but the result was nevertheless the 
same ; and in order to avoid any error that might be caused 
by some accidental quality of the sound arising from the 
length of the muscle employed, or length of the bones con- 
cerned in conveying the imitative sound to my ear, I made 
the following variation of the experiment. My ear was 
stopped by a cushion pressed upon by the end of a notched 
stick that rested on my foot, and thus conveyed the vibra- 
tion from the muscles of my leg to the ear, along with the 
tremor produced by friction upon the notches ; and still the 
results were nearly the same ; varying in frequency between 
20 and 30 in a second, according to the degree of force 
exerted in the experiment.* 
* The resemblance of the muscular vibrations to the sound of carriages at a dis- 
tance, I apprehend to arise not so much from the quality of the sound as from an 
agreement in frequency with an average of the tremors usually produced by the num- 
ber of stones in the regular pavement of London, passed over by carriages moving 
quickly. 
If the number of vibrations be supposed 24 in a second, and the breadth of each 
stone be about 6 inches, the rate of a carriage thus estimated would be about 8 miles 
