65 
clutched together in such a position that the united positive 
currents from both machines should proceed from one polar 
terminal, simultaneously with the united negative currents 
from the other polar terminal, the sum of the currents from 
the two machines was obtained. On the other hand, when 
the armatures were clutched together in the reversed posi- 
tion, without any change being made in the armature con- 
nections, no current was produced outside the two ma- 
chines. 
These experiments, besides exhibting the necessity of syn- 
chronous rotation, further showed that the armatures must 
also occupy the same relative position in the magnet cylin- 
ders, in order that the combined currents from the two 
machines might be obtained. It now occurred to the author 
to see to what extent the want of synchronism in the arma- 
tures would affect the magnitude of the current. The 
armatures were therefore unclutclied, and allowed to revolve 
independently of each other, in the same manner as when 
the attempt was made to take the combined direct current 
from the commutators. After the alternating current had 
been transmitted through the electric lamp for some time, it 
was found that there was no perceptible diminution in the 
amount of light produced from the carbon points, and that 
the current would melt, very nearly, the same quantity of 
iron wire as when the armatures were clutched together 
On examining into the circumstances attending this unex- 
pected phenomenon, it was first observed that whenever the 
machines were stopped, the pins and holes in the respec- 
tive discs were exactly opposite each other ; and that, 
while the armatures were revolving, the two discs could at 
all times be engaged and disengaged with the greatest 
facility. Moreover, even when the discs were set (before 
starting the machine) a quarter, or half a revolution, out of 
the position in which the maximum amount of current was 
obtained, it was found that, after the armatures had been 
