Plate XIX. illustrates the discharge taking place between a ball 30" diam. and the ground plate. In the former case the discharge is about 3 1/2 feet, in the latter about 3 feet long. These photographs were taken through about half of the full lense opening, nevertheless the discharge is not sharp for although the focusing was carefully effected the wide luminous band on each side of the arc proper, which was referred to, blurs the image. To improve the photographs two more plates were exposed, one the same as plate XVIII., marked XX., showing discharge between a wire and ground plate, and the other, marked XXI., illustrating discharge playing between a ball 18" diam. and the ground plate. In these instances a small opening was used and the images are sharper. To be quite sharp a pin-hole diaphragm should be used. The vibration in these four instances was the normal as before determined, all jars and one turn in primary, 25 throws of switch, very short, flash afterwards.
