194 TROWBRIDGE. — HIGH ELECTROMOTIVE FORCE 
ous. I was interested to ascertain whether the capacity at the 
affected the 
breaking down effect in air and in oil. Without the external capacity, boiled linseed 
oil broke down between two small spheres one millimeter apart, under a difference of 
potential of 20,000 volts. A sheet of microscopic cover glass ^io of an inch in thick- 
ness, however, was not perforated, and a sheet of mica j^ of an inch also withstood 
this difference of potential. When a capacity of 10,000 electrostatic units was con- 
nected to the terminals of the battery, no difference in the breaking down effect could 
be detected. 
If, instead of the high resistance of the wooden table, a water resistance is inter- 
calated between the poles of the battery and the Leyden jars, the same phenomenon 
is observed. The jars charge slowly to a sufficient potential, then discharge, and this 
discharge takes place with remarkable regularity ; the smaller the resistance inter- 
posed, the more rapid the rate of discharge. The time of discharge can be regulated 
pleasure by means of 
2trical clock. 
Q ~. ^-v. v^v, „* ".OVllCUg 
d the battery serves as a species of 
The problem of a practical form of resistance early became an important one. I 
have used cadmium iodide resistances recommended by Hittorf. This form of resist- 
ance is useful for weak currents, but it heats under powerful currents. At one time 
it was thought that graphite resistances might be useful; accordingly a bank of 
graphite cylinders, made of compressed powdered graphite, were mounted on quartz 
columnar crystals. It was speedily found that these resistances had a large temper- 
ature coefficient, and moreover developed a large back electromoti 
ing to 500 or 800 volts when a difference of 20,000 volts was applied to the bank of 
resistances. I accordingly adopted a resistance of running water 
for 
having no temperature coefficient 
which was very 
At the base of a lare 
flowed out through a long horizontal 
tube. A Wire introduced into this tube could be pushed in or out of it, and could 
thus modify the resistance in the circuit. A milliamperemeter introduced in the cir- 
cuit with the water resistance gave perfectly steady readings. 
The periodicity exhibited by the battery in charging condensers through large 
resistances « analogous to the periodicity shown by the battery in the recovery of 
the cells after each momentary 
When the jmort circuits are repeated 
in reguar success the striking distance of course diminishes, and a.so the d„ 
o winch the flaming discharge can be extended; finally, such a point is reached that 
the tlaming discharge disappears, and the hitter v ««™ a * v i i e 
, . , , , .. . \\. ' uie Datt eiy proceeds to discharge by means of 
bright white sparks resembling condenser diselmiw* ti • u • i 
ucusci uiscnaiges. this phenomenon is due to a 
