AvGuST 25, 1899. ] 
in which the waves are sustained in an un- 
broken series, and we employ as the source 
of energy a continuous current circuit. It 
shows that we may continuously supply 
energy to an oscillating system and so keep 
up the amplitude of electric oscillations, 
the frequency of which is that due to the 
capacity and inductance of the part of the 
¢ircuit in which oscillations are set up. 
While, in the forms of high-frequency ap- 
‘paratus alluded to, we may obtain almost 
any differences of electric potential up to 
millions of volts, assuming the apparatus 
Jarge enough for the work, we do not get a 
sustained separation of positive and nega- 
tive charges, as in the static machine, or in 
a less complete degree with the inductive 
coil. Professor Trowbridge, of Harvard, 
has, however, made use of large Planté 
rheostatic machines, the condenser plates 
of which are charged in parallel from 10,- 
000 small storage cells connected in series. 
The discharge of the condenser plates is 
effected after they are connected in series 
by a suitable connection changing frame 
moved for the purpose. Very high poten- 
tial discharges are thus obtained and the 
polarity is always definite. It is manifest 
that the size of the apparatus and the per- 
‘fection of its insulation determine the pos- 
sible performance. The objection to such 
‘an apparatus for experimental research or 
demonstration is the large rumber of cells 
required and the complicated arrrangements 
of circuits for charging them. I have, how- 
ever, recently succeeded in removing all 
necessity for the presence of charging cells, 
-and have produced what may be termed a 
dynamostatic machine which is worked by 
power or by current from a lighting circuit, 
either continuous or alternating, and may 
replace a static machine. It is, of course, 
not dependent upon the weather. I trust it 
may be of sufficient interest to merit the 
following brief description: A small elec- 
tric motor hasin addition to its commutator 
SCIENCE. 248 
a pair of rings connected to its armature 
winding for obtaining alternating currents. 
The shaft of the motor drives synchronously 
a revolying frame bearing connections 
which, as in the Planté rheostatic machine, 
connect a series of condenser plates alter- 
nately in parallel for charging and in series 
for discharging at, high potential. A small 
oil-immersed step-up transformer has its 
primary connected to the brushes bearing 
upon the two alternating current rings of 
the motor, and its secondary, giving say 
20,000 volts, is periodicaily connected to 
the condenser plates while in parallel, by 
means of the revolving connection frame. 
The adjustment is such that only the tops 
of the alternating waves or their maxima 
are used to charge the condenser plates, 
while, also, those halves of the waves which 
are of the same polarity are alone used, the 
others being discarded or left on open cir- 
cuit. The apparatus may be driven by 
power, in which case the electric motor be- 
comes a dynamo, exciting its own field and 
supplying alternating current to the pri- 
mary of the step-up transformer, or suit- 
able alternating currents may drive it as a 
synchronous motor. Such a machine, run 
by continuous currents and having only 
eleven plates, gives sparks between its 
terminals over twelve inches long in rapid 
succession. It can be built cheaply, and is 
a highly instructive machine from the trans- 
formations it illustrates. 
The machine is also arranged by the ad- 
dition of a simple attachment, so that it 
may be used to charge insulated bodies, or 
to charge Leyden-jar condensers or the like, 
replacing the ordinary static machines. It 
might, in fact, be used to charge a second 
range of condenser plates in another rheo- 
static machine to a potential of 100,000 
volts, for example. These, after coupling 
in series or cascade, might be made to yield 
potentials beyond any thus far obtained. 
The interest in such experimental ap- 
