Page:Collected Physical Papers.djvu/387

Rh shown in the following curve (fig. 117) which gives the latent period of the pulvinus of Mimosa. The writer

was tuned to vibrate 200 times in a second, and the interval between successive dots therefore represents 1/200 of a second. It is not difficult to measure one-fifth of the distance between successive dots, and calculation can therefore be carried into thousandths of a second. In the present case there are 15.2 spaces between the stimulus and the initiation of response. The latent period of the specimen is therefore 0.076 of a second. The average value of the latent period of the pulvinus of Mimosa is found to be 0.1 second.

The complete apparatus is shown in figure 118. An electrical shock was in the following experiment applied on the petiole at a distance of 30 mm. from the pulvinus, at the instant marked by the vertical line (fig. 119). The frequency of vibration of the writer was 10 per second. The interval between stimulation and the beginning of response is 16.2 spaces, or 1.62 seconds. A repetition of the experiment gave the same result. Stimulus was next applied directly on the pulvinus and the latent period was found to be about