92 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
15 seconds. It will be seen that the central spindle has become bifurcated about 
midway. 
Distance X 3=1 , 74 inch, pressure 191*3 man., 251,711 M, current 0*04060 W, 
depression 17 man., total pressure 208*3 man. ; ratio of increased pressure 1*089. 
The arc is represented in fig. 3 from a photograph in 15 seconds. The bifurcation 
is apparent in this also. 
Distance X 4 = 2*32 inches, pressure 142‘6 man., 187,631 M, current 0*04474 W, 
depression 19 man., total pressure 161’6 man. ; ratio of increased pressure IT33. 
The arc is represented in fig. 4, in which the central spindle is broken up into 
several luminosities. 
Distance X 5 = 2*9 inches, pressure 112*6 man., 148,157 M, current 0*03459 W, 
depression 19 man., total pressure 131'6 ; ratio of increased pressure IT69. The 
arc is represented in fig. 5 from a photograph in 15 seconds ; in this the central 
spindle is split up into bright entities connected by less bright portions. 
Distance X 6 = 3*48 inches, pressure 99*4 man., 130,789 M, current 0*03071 W, 
depression 21 m.m., total pressure 120*4 man. ; ratio of increased pressure 1'211. 
The arc is represented in fig. 6 from a photograph in 15 seconds. The luminous 
entities still seen, but are less marked. 
Distance X 7 = 4*06 inches, pressure 85*9 m.m., 113,026 M, current 0*03259 W, 
depression 22 man., total pressure 107*9 m.m. ; ratio of increased pressure D256. 
Fig. 7 from a photograph in 15 seconds. The central spindle is divided into two 
luminosities, with a tendency to form a third near the negative. 
Distance X 8 = 4*64 inches, pressure 71 *6 m.m., 94,210 M, current 0*02693 W, 
depression 22 man., total pressure 93'6 man. ; ratio of increased pressure 1*307. 
Fig. 8 from a photograph in 15 seconds. The central spindle nearly of the same 
character as fig. 7. 
Distance X 9 = 5*22 inches, pressure 65*5 m.m., 86,184 M, current 0*02693 W, 
depression 22 man., total pressure 87*5 m.m. ; ratio of increased pressure 1*336. 
Fig. 9 from a photograph in 15 seconds. The bright entities show a tendency to 
break up into less bright portions. 
Distance X 10 = 5*8 inches, pressure 64*4 man., 84,737 M, current 0*03071 W, 
depression 20 man., total pressure 84*4 man. ; ratio of increased pressure 1*310. 
Fig. 10 from a photograph in 15 seconds. The arc resembles that seen in fig. 9. 
Distance 5*8 inches, pressure 4 man., 5263 M, current 0*02544, a single nearly 
globular luminosity about 1 inch in diameter near the positive. The negative 
terminal completely surrounded with a brilliant purple glow. 
Distance 5*8 inches, pressure less than 4 man., but could not be exactly observed, 
current 0*02544. Near the positive three distinct strata had formed. 
The curve of the discharge between two points in air, with a constant number of 
cells, the distance increasing as 1, 2 . . . 10, and the pressures diminishing, is shown 
in fig. 83, 
