no RESEARCHES ON IRRITABILITY OF PLANTS 



(loo D.V.) and the resonant vibration in the recorder 

 induced by it. This latter had been previously tuned to 

 give exactly loo double vibrations in a second. A light 

 aluminium stylus attached to the tuning-fork traced a 

 sinuous line on a falling plate of smoked glass. The top 

 of the vibrating recorder was so adjusted as to make suc- 

 cessive dots during its vibration, simultaneously with the 

 tuning-fork tracings. It will be seen from the record 

 (fig. 65) that, corresponding to the crest of each tuning- 

 fork wave and slightly to its right, we have a dot. The 

 record given represents a period of fourteen one-hundredths 

 of a second, there being fourteen crests made by the tuning- 



FiG, 65* — Simultaneous record of vibrating-recorder and 

 100 D.V. tuning-fork exciter. 



fork time-marker, and exactly coincident with these are 

 the fourteen dots made by the vibrating recorder. The 

 interval between any two dots, therefore, is an accurate 

 measurement of one-hundredth part of a second. If the 

 plate be moving at a uniform rate, the interval between 

 these dots will be uniform. But the accuracy of the time- 

 measurements in the curve is independent of the rate of 

 movement of the plate, for we calculate not by the distance 

 but by the number of the dots. In the present figure the 

 record was made on a plate which had been released and 

 during its fall was acquiring increasing speed. The tuning- 

 fork waves are thus gradually broadening out, and in exact 

 correspondence to this the intervals between the dots are 

 lengthening. When the phonograph motor which lets 

 down the plate is just released, there is a short interval 

 during which both that and the dependent plate are 



