213 
close the circuit. Furthermore the experiment must be stopped, as 
soon as the plant makes nutations, or grows in a wrong way. 
Therefore the platinum strip is narrow and allows but an excursion 
of the plant-top, less than 1 m.M. 
The brass piece (8) has been mounted on a hexagonal brass prism 
(11) that runs trae up and down in a well-fraised closed bearing 
(12). This prism (11) is linked by means of an internal strong spiral 
spring with a split-nut (13). In order to get a straight up and down 
movement this nut (18) runs by means of side-wings (14) in slits 
(15). The precision-micrometer-screw (16) runs in the nut (18). In 
the direction of the screw is saved a cylinder of larger diameter 
(30). Both screw-axis and cylinder (80) fit in a block (29). The 
turping of the serew-axis will raise split-nut (18), prism (11) and 
the brass piece with contact-device (8). At the lower end of the 
— serew-axis under the block (29) a cogwheel has been mounted with 
100 teeth (17) at such a rate that the contact is raised, when the 
wheel is turned in the direction of the sharper edges of the teeth. 
In the beginning stage of the work, an energic electro-magnet 
f 
we 
No = 
RAS 
ee tg NS 
— 
22 
Ny, 
ea 
Fig. 2. Explanation in the text. 
