Chemistry and Physics. 323 



to a greater distance than the anticipated striking-distance and 

 gradually approached until the spark passed. The discharger 

 was then detached from the battery, and after reading the scale, 

 connected with a separate battery of 10 cells with a detector-gal- 

 vanometer in circuit. The terminals were again appi-oacbed until 

 the motion of the galvanometer indicated contact between them. 

 The scale was again read, and the chanace in reading gave the 

 required length of spark. With 600, 1200, 1800 and 2400 cells 

 the striking-distances were found to be -0083, -0130, -0:^5 and 

 •0535 inches. These numbers are nearly proportional to the square 

 of the number of cells, which would give the distances 0033, 0132, 

 •0528. The length of spark is much influenced by the form 



volving c 

 mutator, or a double key dischai-ger. 



When the point was negative, a glow in form like a paraboloid 

 was seen surrounding it long before the spark passed, and as the 

 distance was diminished gradually extending to the positive ter- 

 minal. With 1800 cells the glow was seen at a distance of -0545 

 and with 2400 cells at a distance of '0865 inches. Moreover 

 when the disc was positive it became covered with a peach-like 

 bloom which became stronger in the center as the terminals were 

 approached, giving rise to Newton's rings. This effect was next 

 studied with the whole series of 5640 ceds. The glow was now 

 visible at 1-073 in. and the spark passed at -139. Replacing the 

 flat disc by one that was slightly convex the glow occurred at 

 1'124 in. and the spark at -140. Reversing, the current gave 

 sparks of -154 and -164 in. 



To ascertain whether a current really passed when the glow 

 appeared, vacuum-tubes were interposed when they were illumin- 

 ated even before the glow appeared. Of course the striking dis- 

 tance was in this case shortened. With a hydrogen tube having 

 a resistance of 190,000 ohms the glow occurred at 939 and the 

 spark at -092 inches. A 31-inch tube was brilliantly illuminated 

 when interposed between one terminal and the battery, when the 

 rminals were separated to the extreme range of the discharger ( 

 ■''■"■'" ■ • "' the ] • - - 



Considei 



and before any glow was visible at the negati^ 

 I current was obtained with the negative point 5'] 

 plate 6 in. in diameter, 

 experien 



ance of the tubes, and it soon appeared that this resistance rap 

 increased as the current passed. After a time, however, 1 

 recovered their original resistance. Ultimately it was foun. 



be better to discard the indications of the i 



n the appearance of a luminosity in the tubes placed 

 )f Wheatstone's bridge as soon as the insertion of a 

 distance was made in the other. A curious conclusion 

 Hu the law that the length of spark is proportional to 

 f the number of cells, if it proves to be correct. One 

 ive a s])ark about -0000000 1 in. long while a hundred 



