1308 
Now the purpose is to record the duration of period 1 every time. 
The simplest method would be, to make the switch give a mark on 
a revolving drum at each changing over, and next to measure the 
distances of those marks and make a graphic of them. A similar 
method has already been applied by Barus and by LatpLaw and 
Kniaut, who employed drums, revolving rather quickly and falling 
simultaneously, because otherwise the marks would come too close 
together for them to be able to judge the distances. 
The recording-apparatus to be discussed here, has been constructed 
thus, that it gives the required data directly in a survey on a slowly 
revolving drum, so that the modifications in the degree of aperture 
of the stomata, for instance during 24 hours can be read, without 
measuring or copying. 
It consists firstly of a recording drum, turned round by the 
clockwork U, in 24 hours (see fig. 1 at the top). 
The tracing-pencil (11) is fastened to a trolley (12), which can be 
moved on rail parallel to the descriptive line of the cylinder, being 
attached with a cord to the disk (18), which is fixed on one shaft 
with the cog-wheel T, of the second clockwork U,. T, however is 
not constantly in connection with the rest of the cog-wheels of U, 
In fact, the cog-wheel T,, that has to transmit the motion of the clock- 
work to T,, does not turn in the frame of the clockwork, but in 
a separate lever, which can be moved round the pivot 14 to 
a small extent by alternate attraction of the cores of soft iron of 
the solenoids S, and S, If 8, pulls down, T, goes up, the 
motion of T,. is transmitted to T, and the trolley is drawn to the 
left with a certain speed. If next 8, pulls, T, goes down, T, is 
released and the trolly is drawn back to zero by the weight 15. 
The intention with this arrangement is, that the trolley is only taken 
along by the clockwork during the period 1 of the porometer, which 
is to be recorded, and that during period 2 it has an opportunity 
of running back to zero, to recommence its uniform movement with 
the next period 1. The longer period 1 lasts, the longer the clock- 
work continues pulling uninterruptedly and the longer therefore grows 
the line, traced by the pencil towards the left. In this way the left 
extremities of the lines thus obtained, give a distinct picture of the 
course of the durations of the periods 1, i.e. of the degree of aperture 
of the stomata. 
For the changing over of the cog-wheels at the exact time the 
automatic switch W cares, which itself is indeed changed over at the 
alternation of the two periods. To its shaft namely some other iron 
forks have been fixed insulatedly and these serve to close circuit 
