﻿BOTANICAL GAZETTE 



the top was closed by 



transparent fluorite plate E. The Schu- 

 mann rays were emitted through this 

 fluorite plate. As will be seen from the 

 figure, the tube was so designed that 

 the internal capillary was brought as 

 near the fluorite window as possible 

 without excessive heating of the 

 window. This arrangement made it 

 possible to expose the organism very 

 near to the source of light. The dis- 

 charge tube was excited by a ^-kilowatt 

 transformer manufactured by the Clapp 

 Eastham Company. The transformer 

 worked on a no- volt alternating circuit 

 of 60 cycles. A variable resistance in 

 the primary circuit was adjusted so 

 that about 0.8 ampere flowed through 

 the primary of the 

 transformer. The 

 ^ current through 

 the discharge tube 

 was 16-18 milliamperes. No capacity, 

 beyond that due to the leads, was in- 

 cluded in the discharge tube circuit. 



The primary circuit of the trans- 

 former was operated by a relay working 

 on a battery circuit which was controlled 

 by an ordinary telegraph key. The 

 relay circuit had connected with it 

 another circuit which moved the pens 

 on a chronograph. From the chrono- 

 graph record the exact length of any 

 exposure could be determined. The use 

 of the relay circuit and telegraph key 

 made it possible to operate the dis- 

 charge tube without the risk of coming in contact with lines carry- 

 ing currents of higher voltages. This was important when the 



Fig. i. — Discharge tube used 

 for generating Schumann rays: 



A , ring electrodes of aluminum; 



B, C, terminals connecting with 



(£, M, F); D, capillary for 

 increasing the current density; 

 E, fluorite window; F, glass 



