RADIOTELEGRAPHY—FLEMING, 167 
something of the order of 5:1 of even 20:1. In this case the con- 
denser is charged by means of an induction coil or transformer, and 
discharged across a spark gap, and this discharge consists of inter- 
mittent trains of electric oscillations with a periodic time equal to 
the free natural period of the oscillatory circuit. These discharges 
are made to succeed each other from 50 to 600 times a second, by 
using an induction coil with an appropriate interrupter, or else an 
alternator and a transformer. If the 
arc method of exciting the oscillations 2, Ey 
is employed, then the ratio of capacity es alga 
to inductance must be much smaller and 4/3, a 23 
the oscillations are excited in this cir- [8 a 
cuit by a continuous current arc worked é 
with a voltage from 200 to 400 volts or = x 
more, the arc being traversed by a 
strong magnetic field and generally be- as oF 
ing placed in a chamber kept free from z B 
oxygen. The oscillations set up in the Fre. 6. 
condenser circuit are then persistent or unbroken. The oscillations 
are excited in the antenna by coupling it inductively or directly with 
the condenser circuit (see fig. 6). If the former method is employed, 
then an oscillation transformer is used consisting of two coils of wire, 
one coil being inserted in the condenser circuit and one in the an- 
tenna circuit, and according as these coils are near or far apart, they 
are said to be closely or loosely coupled. These two circuits have 
then each their own natural period of electric vibration, like tuning 
forks, and they have to 
be adjusted to syntony. 
It is well known that 
under these conditions 
oscillations set up in 
one circuit immediately 
create oscillations of 
two frequencies in both 
circuits. This action 
can be easily  illus- 
é trated by two pendu- 
lums which are of the same length and are hung side by side on 
a loose string distinguished by red and blue bobs. If one pendu- 
lum is set swinging, it imparts little jerks to its other and sets 
the latter in motion, but to do this the first must part with its 
own energy, and hence is gradually brought to rest. Then the opera- 
tion is repeated in the reverse direction. The motion of each pendu- 
lum may then be represented by the ordinates of a curve such as those 
in figure 7. This kind of motion can, by a well-known theorem, 
45745°—sm 1909——12 
Blue Pendulum 
Hig. 7. 
