262 Prof. Riess on Electric Pauses. 



2^ inches thick could be moved up to contact with the brass 

 sphere, or withdrawn from it to a distance of inches. The 

 collar was connected by a wire with a general discharging train, 

 and with the same train the rubber of the machine was also con- 

 nected. On the end of the brass bar a truncated cone of brass 

 was screwed, which is shown in section in fig. 2, and the dimen- 

 sions of which were ab 8i, be 2|, cd 7j, and 

 de 1^ lines. The conical portion of the piece 

 was at first more complete, but was gradually 

 blunted with great care, until the phsenomena 

 now to be described showed themselves. This 

 portion of the work is tedious, but it is indis- 

 pensable. When the conductor was charged 

 positively by the continuous turning of the 

 machine, the following series of sparks was 

 obtained by the gradual augmentation of the distance between 

 the cone and the sphere. 



Distance of the Electrodes in inches, 



1 l\ 11 If 2 2i 3 31 4 4i 



s S S S S 



The continuous passage of sparks took place at the distances 

 marked S ; single sparks occurred at the place marked s ; and 

 where neither of these letters occur no sparks were observed. 

 Hence in this experiment sparks 1 an inch and 21 inches in 

 length were obtained, but no spark of a length intermediate be- 

 tween those. The pause-distance, as it has been named by Gross, 

 extended to 2 inches, and retained this magnitude almost un- 

 changed in all repetitions of the experiment. 



When the machine was in very good action, single sparka 

 were observed f of an inch in length ; but to balance this, none 

 were seen of the length of 2^ inches ; the pause-distance had, 

 so to say, shifted its position without changing its magnitude. 

 When the electrodes are viewed from a point not too near them in 

 the dark, while they stand at the shortest pause-distance asunder, 

 a very short and slender negative brush is observed at the end 

 of the cone, and on the adjacent surface of the sphere a bluish 

 glowing spot. When the electi-odes are gradually separated to a 

 greater distance, the brush remains almost vmchanged, but the 

 glowing spot increases considerably in magnitude. If while they 

 remain within the pause-distance the hand or any other conductor 

 be caused to approach the electrodes, the pause is annulled and 

 the sparks pass. When a small plate was fixed about 3 inches 

 below the electrodes, sparks of all the lengths above stated could 

 pass : the pause was not observed. 



