84 DE. S. R. MILNER ON THE NATURE OF 



lines (3612, 3600, 3584) which forms the strong diffuse streamers at the extreme bottom of the spark. 

 The remaining lines visible in the prints are the groups (4622, 4611) at the extreme top of the spectrum, 

 with the sharp strong streamers of (4529, 4511, 4478) just below it, an unidentified line of approximate 

 wave-length 4200 a little above the arc line, and (3713, 3701) a little below it. These groups possess a 

 duration of 12 micro-seconds and they show streamers which are more sharply defined and which die out 

 more rapidly than those of the first-mentioned group, but the distinction between spark and condensed 

 spark lines appears to be less marked with aluminium than with the other metals. 



Bismuth. 



Fig. 11. Capacity 0-0223 microfarad, no inductance, velocity 220 metres per second. 



Fig. 12. Capacity 0'0223 microfarad, inductance 40 microhenries, period 6'0 micro-seconds, velocity 

 GOO metres per second. 



Fig. 13. Capacity 0'0223 microfarad, inductance 95 microhenries, period 9 '14 micro-seconds. 



Fig. 14. Capacity 0'0223 microfarad, inductance 170 microhenries, period 11 '7 micro-seconds. 



The bismuth figures are described in the text, p. 78. The streamer dots apparent in the course of the 

 arc line bands 4722, 4120 are not due to the arc lines but to spark lines, (4797, 4750) and 4080, which 

 show through them. The equality of the velocities in the streamers corresponding to the various lines is 

 plainly shown in the negatives. The streamers in the condensed spark lines are fan-shaped, they are 

 quite narrow at the pole and spread out as they recede from it, while those of the other lines have a 

 broader base. This is interesting as it shows that the vibrations of the condensed spark lines are only 

 induced just at the very centre of the oscillation period when the current and electric force are at their 

 maxima. 



Durations in fig. 1 1 : 



Arc lines 105 micro-seconds, spark linos 18 micro-seconds, condensed spark lines 9 micro-seconds. 



Cadmium. 



Fig. l.">. Capacity O'OIOG microfarad, no inductance, velocity 450 metres per second. 



Fig. 16. Capacity 0'0223 microfarad, inductance 95 microhenries, period 8'7 micro-seconds, velocity 

 1000 metres per second. 



Fig. 17. Capacity 0'0223 microfarad, inductance 95 microhenries, period 9'2 micro-seconds. 



Fig. 18. Capacity 0'0171 microfarad, inductance 260 microhenries, period 13'2 micro-seconds, velocity 

 850 metres per second. 



All the lines of cadmium show the streamers plainly, but there is a great contrast between the sharp 

 streamers of the spark lines and the blurred ones due to the lines which persist in the arc. In spite of 

 their different character the uniformity of their velocities can be seen in fig. 16. 



The following are the more prominent lines visible : 



Arc lines. Duration 67 micro-seconds. 



5085, 4800, 4678. Partly overlapping blurred streamers. 



(3613, 3610). Strong diffuse streamers at the bottom of the spark. Those of (3467, 3466), 

 much fainter, but in the negatives showing an exactly similar appearance to the former, 

 can be just distinguished below them. 

 Spark lines. Duration 10 micro-seconds. 



(5378, 5337). At the extreme top of the spark. The streamers are very sharply defined and 

 visible near the poles only. There appear to be no condensed spark lines. 



