374 O. N. Rood—Nature and Duration of 
Striking distance 2 millimeters.—Form was generally like fig. 
4, merely ten or twelve instantaneous sparks; total duration 
‘0075 sec. Sometimes forms like fig. 7 were seen. 
Striking distance 3 millimeters.—Like the last, with perhaps 
twenty sparks; total duration 0088 sec. Forms like fig. 7 were 
sometimes seen. 
Striking distance 4 millimeters,—Fifteen or twenty sparks; 
total duration ‘0081 sec. 
Striking distance 5 millimeters. —Form same as the last; num- 
ber smaller ; total duration ‘0078 sec. 
“Striking distance 7 millimeters —Same form; total duration 
0067 sec. 
Striking distance 9 millimeters,—Form the same; total dura- 
tion ‘0060 sec. 
Striking distance 10 millimeters.—Same form; total duration 
-0046 sec. 
Striking distance. 12 millimeters.—Same form still; only four 
or five sparks ; total duration ‘0041 sec. 
Striking distance 15 millimeters.—Like the last, consisting of 
two or three sparks, total duration 0020 sec. 
The maximum striking distance was 24°5 millimeters, when 
the discharge consisted of only a simple instantaneous spa! 
an 
It will be noticed that the total duration of the discharge 1 
these experiments was not, as formerly, a maximum a 
a 
een known that the simple induction discharge consists of an 
instantaneous spark which is followed by a violet light, the 
latter lasting during a rather large fraction of a second. This 
is called the aureol, and has been studied by several physicists 
