ON A METHOD OF PRECISELY MEASURING THE VIBRATORY PERIODS OF TUNING-FORKS, 

 AND THE DETERMINATION OF THE LAWS OF THE VIBRATIONS OF FORKS; WITH 

 SPECIAL REFERENCE OF THESE FACTS AND LAWS TO THE ACTION OF A SIMPLE 

 CHRONOSCOPE. 



By Alfred M. Mayer. 



This research was carried on with funds from the Bache endowment to the N'ational Academy 

 of Sciences. Its object was to arrive at a method of preciselj' measuring the vibratory periods of 

 tuning-forliS, and to determine the laws of the vibrations of forks, with the special reference of 

 these facts and laws to the uses of the tuning fork as a chronoscope in measuring small intervals 

 of time. 



The method devised is to make a clock, at each second, flash a spark of induced electricity on 

 the trace made by a style attached to the prong of the vibrating fork F. P, Fig. 1, is the pen- 

 dulum armed with a triangular piece of platinum foil, which, at each second, cuts through a 

 globnle of mercury contained in a small iron cup, .U. This cup is so made that the globule can be 

 regulated as to size and height by means of a screw-collar. Fresh mercury was placed in the cup 

 at each experiment. The tuning-fork F is screwed into a board, H, which is hinged at h. This 

 board rests against a screw-stop, E. C is a cylinder of brass, rotating on an axle, on one end of 

 which is cut a screw, which runs in a nut at T. (See upper figure of Fig. 1.) The end of a prong 

 of the fork is armed with a small triangle of thin elastic copper foil, about --}„ millimeter thick, 

 and weighing only one milligram. The surface of the prong is well washed with ether, and then 

 the foil is cemented to it with shellac. The point of this style just touches the camphor-smoked 

 surface of paper, which tightly and smoothly envelops the cylinder C. The primary coil of an 

 inductorium, I, and the clock (through P, and the globule of mercury, M) are placed in the circuit 

 of a voltaic cell, B. In the secondary circuit of the inductorium is the fork F and the cylinder C, 

 the thickness of the jiaper on the latter separating the point of the style on the fork from the 

 surface of the brass cylinder. The fork is thrown upward, around the hinge /;, vibrated by drawing 

 a bow across a prong; then depressed till the board jB" comes against the stop -B. The cylinder is 

 rotated, and the trace of the fork is made on the paper, as shown in upper figure of Fig. 1. At 

 each second, when the platinum-tipped pendulum leaves the globule of mercury, a spark flashes 

 from the point of the style and makes a single minute and circular white spot on the blackened 

 paper. This spot must be bisected by the trace of the fork. The center of the spot is generally 

 marked by a minute perforation. 



To obtain the results just described, it is necessary to fulfill certain conditions in the experi- 

 ment, which, if neglected by experimenters, they would hastily regard the method as inaccurate. 

 These conditions are as follows: (1) The globule of mercury siiould be small and rigid; that is, 

 it should not vibrate when the platinum tip cuts through it. This condition is attained bj' screwing 

 up the collar on the small cup M till only a small portion of the mercury is above the upper face 



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