But very much quicker or slower rates may easily be obtained by means of the different-sized pulleys. The spot of light from the galvanometer is thrown down on the paper by an inclined mirror. The movement of the galvanometer spot takes place at right angles to the direction of motion of the paper. There is a guide rod at right angles to the motion of paper, along which the recording pencil is moved. The excursion of the galvanometer spot can thus easily be
followed with a pencil, and it is quite easy to do this, when the fluctuation period is more than 2 seconds. In the experiments to be described, this period varied from 2 seconds to several minutes. A curve is thus directly obtained, with conductivity or electromotive variation as ordinate, and the time as abscissa. The curves given in the accompanying papers are exact copies from the direct records.
4. Transition of a Molecular Receiver from Non-recovering to Self-recovering Condition.
When a substance is strained by radiation there is produced a sudden variation of conductivity. The substance will recover from the strained condition (1) if it has not been overstrained by an excessive stimulus, or (2) if its electric elasticity be very great. I have found in general that on careful adjustment of a receiver there is a tendency to self-recovery if the intensity of incident radiation is not too strong. In the case of substances which are, electrically speaking, highly elastic, such as K, there is an automatic recovery even when
