THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XII. — Magnetic Field and Coronal Streamers / by 

 John Trowbridge. 



In the course of an investigation of the phenomena pre- 

 sented by electric discharges in strong magnetic fields, it was 

 soon apparent that phenomena appear at high voltages together 

 with strong steady currents which do not manifest themselves 

 at lower voltages and lesser currents. I have, therefore, 

 employed comparatively large tubes ; voltages ranging from 

 3000 to 8000 between the discharge terminals ; currents from 

 5 milliamperes to 20 milliamperes. 



The most practical form of resistance I have used is a col- 

 umn of running tap water under constant pressure in glass 

 tubes of suitable diameter. Graphite resistances mounted on 

 quartz have a large temperature-coefficient, and also a remark- 

 able counter electromotive force. The glass tubes containing 

 rarified air ranged from cylindrical tubes 80 cm long, 4 cm internal 

 diameter to cylindrical tubes 48 cm long and 10 cm internal diam- 

 eter. The experiments described in this paper were per- 

 formed with tubes 30 cm long and 4 cm internal diameter. 



At pressures varying from l cm to l mm the cathode light on a 

 circular aluminum plate 3 em in diameter forming the pole of a 

 powerful magnet, the magnetic lines of which are directed 

 along the line of electric discharge, is driven to the circum- 

 ference of the disc, forming to the eye an apparently steady 

 circular discharge. When the tube, however, is covered with 

 black paper, exposing only the light of the disc, and this light 

 is examined in a revolving mirror, it is seen that we have an 

 interesting case of unipolar rotation. Fig. 1 is a photograph 

 taken of the reflection in the revolving mirror. The glass 



Am. Jour. Sci.— Fourth Series, Vol. XXI, No. 123.— March, 1906. 

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