168 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
be resolved into the sum of two oscillations of different frequen- 
cies. Hence, each pendulum may be said to possess two rates of 
vibration. The same thing happens in the case of two closely 
coupled syntonic electric currents. If one circuit has free oscillations 
set up in it, the action and reaction of the circuits generates oscilla- 
tions of two frquencies. Accordingly, when an antenna circuit is 
coupled to a condenser circuit, we have oscillations of two frequencies 
set up in it, and waves of two wave lengths radiated from the an- 
tenna. The presence of these two waves can be detected either by 
measurements made with the cymometer or by an oscillograph 
vacuum tube. In the first case all that is necessary is to place a 
cymometer in proximity to the antenna and vary its oscillation con- 
stant. It will be found that there are two settings of the handle for 
which the Neon tube glows brightly, and the scale of the instrument 
will indicate the wave 
lengths of the two waves 
respectively. Some instruct- 
A2= 1060 metres 
C, 
= 0'0043 mfds. lve measurements of this 
= 0'0048 mf ; 
kind have been made by 
Prof. W. G. Pierce in a re- 
cent research, and he has 
shown that the wave lengths 
given by the formule which 
can be deduced from the 
theory of the operations are 
in agreement with actual 
measurements (see fig. 8). 
Another striking confirma- 
tion can be obtained by the 
200 400 600 800 1000 1200 1400 1690 oscillograph vacuum tube, 
Fic. 8.—Pierce’s eee inductive coupling. invented 2 Baa Gomes. 
~ of the Reichsanstalt, Ber- 
lin. This consists of a glass tube having two strip electrodes in 
it nearly touching, which are made of nickel or aluminum. The 
tube is filled with pure nitrogen and exhausted to a pressure of 
about 10 to 20 mm. If such a tube has a high voltage applied 
to its terminals, a glow light extends along the electrodes, the length 
of which varies with the electromotive force. Hence, if the tube 
is connected to a circuit in which an oscillatory discharge is taking 
place, the glow light along the tube will rapidly extend and contract. 
If the electrodes are examined in a revolving mirror, making from 
fifty to a hundred turns a second, the images of the glowing elec- 
trodes corresponding to each oscillation will be separated out, and 
if the oscillations are persistent or undamped, we see a series 
of short bright lines alternately above and below a centrai line. 
eee 
+ Asty/(R-)E+ 4S 
