1879.] 



1 he Chloride of Silver Battery. 



289 



it after each set, partly on account of the variety of experiments it is 

 intended to make with it ; consequently they describe only a few of 

 the first results hitherto obtained. 



For Example in Air. 



Pressure 3 m.m., 3,947 M, 6,300 cells. Two luminosities were 

 formed, the ring negative being surrounded with a nebulosity which 

 completely filled the end of the tube. The tube glowed brilliantly 

 with a blue fluorescent light, which proved to have great actinic 

 power. A dry-plate photograph obtained in 5 seconds records a very 

 curious phenomenon, namely, that the outer boundary of the 

 luminosity appears darker than the tube. It is to be remarked that 

 while the discharge was reddish (nitrogen), the fluorescence of the 

 tube was blue ; the effect appears to be due to the absorption of a 

 portion of the fluorescent light emanating from the back of the tube 

 in passing through the red luminosity. The effect was quite un- 

 expected, and it was thought at first that it might have arisen from 

 some peculiarity in the development of the dry plate ; it was not 

 therefore until the result had been confirmed by other photographs that 

 they ventured on the explanation above given. 



The paper closes with the following conclusions : — 



1. For all gases there is a minimum pressure which ofers the least 

 resistance to the passage of an electric discharge. After the minimum has 

 been reached, the resistance to a discharge rapidly increases as the 

 pressure of the medium decreases. With hydrogen the minimum is 

 0*64 m.m., 842 |\/| ; at 0'002 m.m., 3 it is as great as at 35 m.m., 

 46,000 M- 



2. There is neither condensation nor dilatation of a gaseous medium in 

 contiguity with charged terminals. 



3. When the discharge takes place there is a sudden dilatation of the 

 medium in addition to and distinct from that caused by heat. This 

 dilatation ceases instantaneously when the discharge ceases. 



4. The potential necessary to produce a discharge bshveen parallel flat 

 surfaces at a constant distance and, various pressures, or at a constant 

 pressure and various distances, may be represented by hyperbolic curves. 

 The resistance of r the discharge between parallel flat surfaces being as the 

 number of molecides intervening between them. 



5. This law does not hold with regard to points. In Fart I it has 

 been shown that the potential necessary to produce a discharge at the 

 atmospheric pressure and various distances is as the square root of the 

 distances, while with a constant potential and various distances, the 

 pressure has to be diminished in a greater ratio than thai of the increase 

 of distance in order to permit a discharge to tah •e place, 



6. The electric arc and the stratified discharge in vacuum tubes are 

 LiwlificoAions of the same phenomenon. 



