﻿BOVIE— SCHUMANN RAYS 



tube was used in connection with a compound microscope, for it 

 was often desirable not to look away from the microscope while 

 operating the discharge tube. 



The discharge tube was placed upright under the stage of a 

 compound microscope, in the place usually occupied by the con- 

 denser and other substage attachments, with the fluorite window 

 flush with the upper surface of the microscope stage. When the 

 discharge tube was in this position the microscope mirror could not 

 be used. Hence it was necessary to illuminate the objects under 

 observation by some other means. Various methods were em- 

 ployed: an arc lamp was placed beneath the work table, and by 

 means of mirrors and lenses a beam of parallel light was directed 

 up through the discharge tube; or the objects were lighted from 

 above, either by concentrating the light on the microscope stage 

 with a condensing lens or by using a special vertical illuminating 

 objective. 



The discharge tube was held by a mechanical support so 

 arranged that by moving a lever the discharge tube moved down 

 and away from themicroscope stage. The regular substage attach- 

 ments could then be swung back into operating position. The 

 change from the discharge tube to the substage attachments or 

 from the substage attachments to the discharge tube could be made 

 very quickly, and without interrupting observations through the 

 microscope. 



The Schumann region of the spectrum is a region of general 

 absorption for most substances. But few solids are known which 

 transmit even the longest Schumann waves (26). Air absorbs all 

 except the longer waves, the absorption being due to the oxygen (27). 

 Fluorite is the only substance known which transmits the entire 

 Schumann spectrum. In fact, the Schumann spectrum extends in 

 the direction of short wave lengths only as far as fluorite transmits. 

 It is evident, therefore, that if we wish to expose organisms to the 

 entire Schumann spectrum we can have no substance other than 

 fluorite between the organism and the source of light. Even" air 

 must be displaced by the more transparent fluorite. Occasionally 

 the organisms were placed directly on the fluorite window of the 

 discharge tube; more often a special slide was used. The special 



