296 



< 'rooh r — Influence of a Series Spark 



voltage, the current in the beads would increase with the 

 time, the heads would increase in size and in a short time 

 would combine to form an arc. Detailed observations 

 were made on this point. 



On closing the switch several beads were formed which 

 soon combined into one, much larger and brighter as 

 shown in fig. 10a. This bead seemed to take hold on the 

 wire at a surface irregularity and remain fixed. A bright 

 reddish spot on the wire formed the base of the bead, 



Fig. 10a. 



D 



Fig. 10a. Evolution of beads into the arc. 



while a bright blue-white core extended out from that 

 toward the bright spots on the edge of the observation slot 

 and shaded off into a milky glow or brush. As time pro- 

 ceeded the core grew larger and brighter and the milky 

 glow of the brush reached farther toward the tube, as in 

 B. Soon a faint reddish glow, C, appeared in the gas 

 proceeding from the bright spots on the tube and extend- 

 ing toward the bead. This glow continued to increase in 

 brightness for a short time until the arc D flashed into 

 existence. The arc had a very bright tubular blue-white 

 core surrounded by a hazy reddish glow and extended 



