M oto-excitability in Mimosa . 
763 
overcome by the two independent devices, the Resonant Recorder 1 and the 
Oscillating Recorder. In the former the writer is maintained by electric 
means in a state of continuous to and fro vibration, about ten times in a 
second. There is thus 
no continuous contact 
between the writer and 
the smoked glass surface, 
friction being thereby 
practically eliminated. 
The writer in this case 
taps a record, the suc- 
cessive dots occurring- 
at intervals of *i second. 
The responsive fall of 
the leaf is rapid, hence 
the successive dots in 
this part of the record 
are widely spaced ; but 
the erection of the leaf 
during recovery takes 
place slowly, hence the 
recovery part of the 
curve appears continu- 
ous on account of the 
superposition of the suc- 
cessive dots. The ad- 
vantage of the Resonant 
Recorder is that the 
curve exhibits both re- 
sponse and recovery. 
This apparatus is ad- 
mirably suited for ex- 
periments which last for Fig. 2. The Oscillating Recorder. Petiole attached to one 
r . . . arm of lever L by thread. The writer traces response-record on 
a tew hOUlS. Inere IS, glass plate G, which falls at definite rate by unwinding of the 
however some draw- clock wheel w. m, magnetic device for maintaining to and fro 
’ . . oscillation of recording plate. R, plunging rod for periodic 
back to its Use in ex- closure of exciting current. C, clockwork. 
periments which are 
continued for days together. This will be understood when we remember 
that for the maintenance of 10 vibrations of the writer in a second, 10 electric 
contacts have to be made; in other words, 36,000 intermittent electric 
1 A complete account of the former is given in my paper ‘ On an Automatic Method of Investiga- 
tion of the Velocity of Transmission of Excitation in Mimosa ’, read before the Royal Society, 
March 6, 1913 (Phil. Trans., B, No. 305, vol. 204). 
