5 
of Muscular Action. 
As a further proof that I was not much deceived in my 
judgment of the frequency of these vibrations, I requested 
two or three of my friends to repeat the same experiment 
for me, and our agreement was such as to confirm me in the 
opinion, that there could be no very considerable error in the 
estimate. 
The greatest frequency that I think I have observed, was 
about 35 or 36 in a second, and the least was as low as 14 or 
15 ; but in attempting to lessen the number of vibrations, 
there appears to be a degree of unsteadiness which prevents 
any accurate measurement of the real number. 
It is very probable, that in cases of great debility the num- 
ber may be even considerably less, and may be the reason of 
that visible unsteadiness, which is known to occur in persons 
enfeebled by age, or much reduced by disease. 
Possibly the foregoing observation may not be altogether 
new to some members of this Society, as it is now about 17 
or 18 years since it first occurred to me, and I was then accus- 
tomed occasionally to mention it in conversation with my 
friends ; but I am not aware that any other person has made 
the same remark respecting the vibratory nature of muscular 
action, although I find that Grimaldi had observed the sound 
that occurs upon stopping the ears, but ascribed it, according 
to the notions that prevailed in his time, to the hurried motions 
of the animal spirits.* 
an hour, which agrees with the truth as nearly as the assumptions on which the esti- 
mate is founded. 
* Vera itaque ratio experimenti prasdicti est, quia in digito et brach'O tbtoque 
corpore continuato aunt mulci motus ac tremores, ob spirituum agitationem hue illuc 
perpetuo accurrentium. Grimaldi, Physicomathesis de Lurmne, p. 383. 
