PHILOSOPHICAL TRANSACTIONS 
I. On the Determination of the Rate of Vibration of Tuning-Forks. 
By Herbert M‘Leod, F.C.S ., and George Sydenham Clarke, Lieut. R.E., Royal 
Indian Engineering College , Cooper s Hill. 
Communicated by Lord Rayleigh, M.A., F.R.S. 
Received January 16,—Read January 30, 1879. 
[Plates 1-3.] 
In a paper in the Proceedings of the Royal Society for 1877, xxvl, 162, when 
describing a new method for determining the speed of machines, we pointed out that 
by the employment of a graduated drum rotating with a known velocity the true 
vibration number of a tuning-fork could be accurately determined. The following 
is an account of the apparatus employed, and subjoined are records of some experi¬ 
ments which have been made on tuning-forks with it, which, in view of the attention 
now being given to the subject, may prove of interest. 
One essential instrument proved to be a good time-measurer. It will be seen in the 
sequel that an electric current is required once a minute, and in the earlier experiments 
a two-day marine chronometer was employed, a key being depressed by hand at the 
end of each minute. So many difficulties, however, arose from its use that it was soon 
rejected and a clock substituted. Near the pendulum two springs were placed 
which, being pressed together at the end of each vibration, made a contact at every 
alternate second. About the 59th second of each minute, a key was depressed 
by hand and held down until the clock completed the circuit. This, though a great 
improvement, was not entirely satisfactory, and endeavours had to be made to eliminate 
entirely all contacts made by hand. This was done by means of a compensated pendu- 
MDCCCLXXX. B 
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