An apparatus has been developed for recording internal friction data in such a manner as to circumvent many of the laborious and time-consuming observations and calculations usually associated with these measurements. As in the conventional method, an optical lever is used. Instead of following the oscillations visually, however, the passage of the beam across the scale is detected by photoconductive cells. The cells are strategically located so that, when their signals are fed through a multichannel switching circuit to the pens of an operation recorder, a plot of the logarithm of the vibrational amplitude against the number of cycles is recorded on the chart. From the definition of the logarithmic decrement δ it can be shown that the slope of this curve is -δ. The apparatus is inexpensive and requires a minimum of maintenance. It has been used for accurate determinations of values of δ from below 0.0001 up to 0.3.