1914] on Plant-Autographs and their Revelations 177 



pull exerted by the motile organ is relatively feeble, and in the 

 movement of the very small leaflets of Desmodium gyrans, or the 

 Telegraph plant, for instance, a weight so small as four-hundredths 

 of a gram is enough to arrest the pulsation of the leaflets. Even in 

 the leaf of Mimosa the friction offered is enough to introduce serious 

 errors into the amplitude and time-relations of the curve. This 

 error could not be removed as long as the writer remained in 

 continuous contact with the writing surface. I was, however, able 

 to overcome this difficulty by making an intermittent, instead of a 

 continuous, contact. The possibility of this lay in rendering the 

 writer tremulous. Fresh difficulties ai'ose which were finally elimi- 

 nated by an invention depending on the phenomenon of resonance. 



The Resoxaxt Recoedeb. 



The principle of my Resonant Recorder depends on a certain 

 phenomenon, known as resonance or sympathetic vibration. In 

 illustration of this we may construct an artificial ear tuned to a 

 definite note. The drum of the artificial ear is made of thin soap- 

 film ; a beam of light reflected from its surface forms characteristic 

 pattern of colour on the screen. To various cries this ear remains 

 deaf, but the apathy disappears as soon as the note to which the 

 ear is tuned is sounded at a distance. On account of sympathetic 

 vibration the artificial ear-film is thrown into wildest commotion, 

 and the hitherto quiescent colour pattern on the screen is now 

 converted into a whirlpool of indescribably gorgeous colour of pea- 

 cock green and molten gold. 



In the same manner, if the strings of two violins are exactly 

 tuned, then a note sounded on one will cause the other to vibrate 

 in sympathy. We may likewise tune the vibrating writer Y, with a 

 reed C (Fig. 3). Suppose the reed and the writer are both tuned to 

 vibrate a hundred times per second. AVhen the reed is sounded the 

 writer will also begin to vibrate in sympathy. In consequence of 

 this the writer will no longer remain in continuous contact with the 

 recording plate, but will deliver a succession of taps a hundred times 

 in a second. The record will therefore consist of series of dots, the 

 distance between one dot and the next representing one-hundredth 

 part of a second. With other recorders it is possible to measure 

 still shorter intervals. It will now be understood how, by the device 

 of the Resonant Recorder, we not only get rid of the error due to 

 friction, but make the record itself measure time as short as may be 

 desired. The extraordinary delicacy of this instrument will be 

 understood when by its means it is possible to record a time-interval 

 as short as the thousandth part of the duration of a single beat of 

 the heart. The complete apparatus for obtaining plant-record is 

 shown in Fig. 4. 



Vol. XXI. (Xo. 108) n 



