238 Mr. C. F. Varley on the Discharge of Electricity [Jan. 12, 



dually reduced. At the commencement it was more than 10,000 megohms ; 

 the upper or small ring was positive, the lower ring was negative. 



The power was so reduced that the faintest possible light only was visible ; 

 in this case the positive wire alone was luminous, whether it were the 

 large or small ring that was positive. No. 2 (PL II.) is a photograph of this. 

 The light was so feeble that, though the experiment was conducted in a 

 perfectly dark room, we were sometimes unaware whether the current was 

 passing or not. An exposure of thirty minutes' duration left, as will be 

 seen, a very good photographic record of what was taking place; this 

 means of viewing light too feeble for the eye may receive other applica- 

 tions. The resistance was then reduced, when the light became much 

 more brilliant, — a tongue of light projected from the positive pole towards 

 the negative, the latter being still almost completely obscure. 



The light around the positive pole was to all of our eyes white, while the 

 projecting flame was a bright brick-red. This bright brick-red, however, 

 possessed great photographic power, as will be seen by photograph No. 3. 

 The negative wire at this stage began to show signs of luminosity. 



As the power was increased, the flame became detached from the 

 positive pole, as shown in photograph 4. 



On still further increasing the power, the positive pole ceased to be 

 luminous, as in photograph 5 ; and on still further increasing the power, by 

 removing the U tube altogether, the phenomena presented themselves which 

 are shown in photograph 6, in which the light surrounded the negative wire. 

 The photograph shows a white flattened hour-glass, apparently detached 

 from the wire ; to the eye, however, the wire appeared to be surrounded by a 

 bright blue envelope | inch in diameter, which did not possess sufficient 

 photographic power to leave a record of itself, while the red portion did so : 

 this photograph was exposed only ten seconds to the light. 



A large condenser was now attached to the battery, and discharged 

 through the tube (the condenser had a capacity of 27 microfarads) ; this 

 was equivalent to a momentary contact with a battery of little or no re- 

 sistance. The flash was exceedingly brilliant to the eye : it could be 

 heard outside the tube with a sharp click ; the eye, however, was so dazzled 

 as not to be able to see its shape. 



Photographs 7 a and 7 b show that the light was confined entirely to 

 the positive pole ; thus, then, as the power is increased from nothing up- 

 wards, the first pole to become luminous is the positive ; secondly, the 

 two poles become luminous ; thirdly, the negative pole alone is luminous ; 

 and fourthly, with an instantaneous discharge, the positive pole only is 

 luminous. The eye and the collodion-plate do not, however, tell the same 

 tale in photograph 6. 



"When the resistance in the U tube was greatly reduced, and a galvano- 

 meter (not very sensitive) was inserted, so that the chief resistance in 

 circuit was that of the exhausted tube, as the potential was augmented cell 



