. Contributions. fork supplied with adjustable masses for regulating the period,and carrying a lens on one prong, was arranged to vibrate horizontallyin front of the wire, so that when a drop of mercury was placed on thewire a Lissajous figure could be viewed through the vibrating lens bymeans of a microscope. A phonic wheel was included in the circuitwith the tuning fork, so that the fork could be accurately rated while Vol. 6. J LOXGITUDISAL VIBRATIOX OF WIRES. 407 the wire was vibrating. The vibration was so slow tliat the lime re-quired for an elastic pulse to travel the length of
. Contributions. fork supplied with adjustable masses for regulating the period,and carrying a lens on one prong, was arranged to vibrate horizontallyin front of the wire, so that when a drop of mercury was placed on thewire a Lissajous figure could be viewed through the vibrating lens bymeans of a microscope. A phonic wheel was included in the circuitwith the tuning fork, so that the fork could be accurately rated while Vol. 6. J LOXGITUDISAL VIBRATIOX OF WIRES. 407 the wire was vibrating. The vibration was so slow tliat the lime re-quired for an elastic pulse to travel the length of the wire was very shortcompared with the perioti of the wire, therefore we may consider thewire to be uniformly strained throughout its entire length at all times. Measurini: the Free , of course, was a forced vibration of the wire, tla- {uricxl wastherefore slightly less than that of the free vibration. It was found,however, that by adjusting so that the fork was slightly too slow, then nAAAAVS/. e, electromagnet actuated by battery s; f, relay; g. mercury cup; j. fine wirf eoldered tomoving system at d; p, stiff platinum-tipped wire for contact with mercury at t- shutting off the current driving the wire, the free period could be obtainedwith considerable accuracy. The free vibration could be observed easily for ^ t min. with the cojjiktwire, about 4 min. with the platinum-iridium wire, and 5 min. with thesteel and phosphor-bronze. In case the period varied with the amplitude,as it did with the copper and platinum-iridium, and also to a slightextent with the phosphor-bronze, the fork was set too slow for smallamplitudes, and too fast for large ones. By means of the micrometermicroscope the amplitude for which the Lissiijous* figure was at restcould be satisfactorily determined. This, however, ncccssilatwi changingthe rate of the fork, and so rating again by the phonic wheel for ever>amplitude measured, an expenditure of time which was partly avoidedby coun
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