Measurement of logarithmic decrements through the measurement of time

The paper describes an arrangement which can be used to measure the period and logarithmic decrement of a damped harmonic torsional oscillation without the need to perform any length measurements. By means of suitably arranged electronic circuits, all measurements are reduced to those of time intervals. These consist of a measurement of the period and of two time intervals which a travelling laser beam requires to sweep past two stationary photoresistances. A suitable procedure for the location of a zero base line is indicated, and it is shown that the residual uncertainty of this operation is the source of the dominant error.The paper contains an analysis of systematic and random errors of the method and mentions that decrements of the order of 0.05 can be measured with a relative error of the order of 0.06%.