Figs. 13-15. Flame non-lurninous, electricity on disc positive. Figs. 19-21. Flame luminous, electricity on disc positive. 
Figs. 16-18. n u n » negative. Figs- 22-24. <> » » » negative. 
Figs. 13-24. Distance of tube from disc constant. jbotowi™ 
