AMERICAN 
JOURNAL OF SCIENCE AND ARTS, 
[THIRD SERIES] 
Art. XIX.— Observations on the duration and multiple character 
ied lashes of Lightning ; by Oaprn N. Roop, Professor of 
Physics in Columbia College. 
ARaGo has classified the different forms of lightning under 
three heads: Ist, linear zig-zag flashes; 2d, flashes appearing as 
a broadly diffused light (sheet lightening, heat lightening), and 
astly, the rarely occurring discharges which are seen as slowly 
7 OVing balls of fire* That the first form is due to the pro- 
duction in the atmosphere of a gigantic electric spark, has since 
tanklin’s time been disputed by no one, and as far as I can 
ascertain, the majority of physicists and meteorologists suppose 
that flashes of the second form are due to the same cause, their 
aght being seen either by transmission through, or reflection 
from, the clouds, 
wefore detailing my own observations on this matter, I wish 
briefly to mention the results thus far obtained by others. 
Among the most important of them is an experiment by Dove, 
Who, in 1835, during a thunder storm, was able, by the help of 
°rs. He supposed that from the appearance abearen by 
the disc when itheentannsd by the flash, the observer wou 
* See Dr. Ernst E. Schmids’ Lehrbuch der Meteorologie; Leipsic, 1860, p. 781. 
t Pogg. Ann., 1835, p. 371. 
Am. Jour. 8c1.—Tarep Serres, Vor. V, No. 37.—Mancu, 1873. 
Il 
