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566
BERKLEY AND MANSBERG
November
fairly close together and the wave shape is not very clearly seen. A better technique is to combine the sweep on the oscillograph with the motion of the film in order to obtain a better utilization of the film area as shown on the upper portion of the recording. Another example of this film-saving technique is shown in Fig. 19, depicting a nerve dying over a long period. In certain cases where we have a phenomenon which takes a considerable time, a fairly good picture of the result may be obtained on a single frame by using continuous sweep and allowing the signal to vary in its normal manner. By increasing the sweep speed, we obtain an expansion of the phenomenon but still use only a single frame. Fig. 20, which is a recording of
Fig. 18 — Two methods of continuous-motion recording.
Fig. 19 — Action potential of a nerve over a long period. (Obtained through co-operation of Dr. H. Grundfest.)
the light build-up of an incandescent lamp, is a typical example of this. The manner in which the build-up occurs can be readily seen ; the fact that the image is broken by the return time of the sweep is of little importance. Where we have a phenomenon which is random, it is necessary to use the film motion as a time base.
The exposure the phenomenon produces depends on the mode of recording. In continuous motion and single-sweep recordings, the spot image traces its path over any point only once and the required exposure, therefore, is the -same as that for a single transient. In complicated cases, as in Fig. 20, where multiple exposure of the steady state is obtained, and only single exposure of the transient portion, the camera setting should be chosen to record the highest writing rate in the phenomenon.