80 Correspondence of J. Nickles. 
“Tf Franklin’s discoveries placed beyond doubt the identi 
of mechanical electricity and lightning, there remained, n 
theless, among the phenomena which accompany storms, 1 
circumstances the explanation of which was yet inaccessib 
science. We must therefore regard as a valuble acquisitio 
meteorology the observation that the spark of the Ruhm 
apparatus consists of two parts—an instantaneous line of 
and an areola of measurable duration. The magnet divides 
latter ; a breath, or any body in motion, draws it out, and 
electric spark thus divided continues its route in these two di 
tions at once, as long as the passage of the current conti 
uninterrupted. 
“In a vacuum, the electric spark develops light, and 
them, and which impresses upon them, at the pleasure of 
operator, those movements of translation or of rotation by means 
of which De la Rive’? has reproduced the appearances observed 
in the Aurora Borealis, justifying, thus, the analogy recogni: 
between the electric light produced in a vacuum and that of 
polar auroras, ; 
“ Glass tubes illuminated by the same means give out ali 
“The working of quarries, the boring of tunnels, the exp! 
of heavy charges in mines, give to-day regular employment bt 
the Ruhmkorff apparatus." Mines had been exploded previouslf 
ni 
of elements which it requires—three instead of one hundr 
the power of its spark, and finally the possibility of exploding 
eight or ten mines at once. In the expedition to China, in 186%; 
the Ruhmkorff apparatus was used to blow up, by means of eig 
mines simultaneously exploded, the peacibal fort of the Pe 
as well as the iron stockade at the bottom of the river.” © ; 
Dumas then reviews the principal applications of electricity 
to Mechanics, such as the automatic break of Achard, the weaving 
