Section III., 1914 [113] Trans. R.S.C. 



The Effect of an Electrostatic Field on a Two Looped Carbon Filament 



Lamp. 



By Dr. A. S. Eve, F.R.S.C. 



(Read May 27, 1914). 



When conducting some experiments on point discharge it was 

 noted that a negative discharge caused the twin loops of a carbon 

 filament lamp to diverge violently and touch the glass sides of the 

 lamp, sometimes until the loops broke, or adhered to the sides and 

 fused. It was possible to produce this effect at a metre's distance, 

 or through a board half an inch thick. On the other hand, the dis- 

 charge from a positive point, if stationary, produced no effect. Some 

 experiments were therefore made to determine the cause of this 

 rather puzzling effect. 



The terminals of the lamp were first earthed, and then the two 

 loops could be made to diverge like the leaves of a gold-leaf electroscope, 

 whenever a charged body, whether positive or negative, was brought 

 near the lamp. 



The lamp was then lit by passing a current through it in the 

 ordinary way. A negatively charged body when brought up to the 

 lamp caused divergence of the loops. A positively charged body, 

 when moved towards the lamp, caused no movement whatever. 

 As the positive body was being moved away, the leaves did diverge, 

 however, and could be left parted asunder at a considerable angle, 

 greater than in their natural position. They could then be observed 

 through red glass with a microscope, to move back slowly to their 

 natural position. 



The return to the rest position could be greatly accelerated by 

 bringing a few milligrammes of radium near the lamp. 



None of the above experiments could be carried out with a lamp 

 with a single loop. 



The festoons of a metal filament lamp bulged outwards in a 

 marked manner, when there was a negative point discharge near it, 

 or when a negatively charged body was moved towards it, or when 

 a positively charged body was removed from its neighbourhood. 

 All these observations may be explained by the Edison effect, or 

 thermionic current of electrons or of negative electricity leaving a 

 glowing filament. It is an example of the valve action investigated 

 by Fleming and explained by him in "Electric Wave Telegraphy," 

 p. 478, 2nd edition. 



Sec. Ill, 1914—8 



