C 3 
XI. Investigations, founded on the Theory of Motion, for deter- 
mining the Times of Vibration of Watch Balances. By George 
Atwood, Esq. F. R. S. 
Read February 27, 1 794. 
Instruments for measuring time by vibratory * motion were 
invented early in the sixteenth -f century : the single pendu- 
lum J had been known to afford a very exact measure of time 
long before this period ; yet it appears from the testimony of 
historical accounts, as well as other evidences, that the bar 
lance was universally adopted in the construction of the first 
clocks and watches ; nor was it till the year 1657 Mr. 
Huygens united pendulums with clock-work. 
The first essays of an invention, formed on principles at 
once new and complicated, we may suppose were imperfectly 
executed. In the watches of the early constructions, some of 
* The ancients, as early as 140 years before Christ (probably much earlier) were 
acquainted with the use of wheel-work in constructing instruments for measuring 
time. “ Denticuli alius alium impellentes, versationes modicas faciunt ac motiones,” 
is the expression of Vitruvi us in describing a machine, one of the principal uses of 
which was to indicate the hour, of the day. Vibrations are no where mentioned or 
alluded to in the descriptions of the clocks constructed by the ancients. Dr. Der- 
ham on Clock-work, p. 86, 4th edit. 
f About the year 1500, according to some accounts., 
t Tycho Brahe is supposed to have used the pendulum in astronomical observa- 
tions. Ricciolus, Kirchrr, Mersennus, and many others, are expressly men° . 
tioned bySTVRMius to have employed this method of measuring time. 
