ELECTRIC WAVE TELEGRAPH Y—FLEMING. irae 
The terminals are connected by a shding inductance and by a con- 
denser. Then, in addition, a long helix of wire is connected to one 
{erminal of the condenser. This helix is tuned to the condenser cir- 
cuit and may be taken to represent the antenna when the apparatus 
is used in wireless telegraphy. If we start the arc, then high-fre- 
quency oscillations are produced in the helix, and by the action of 
resonance the potential at the free ends becomes large enough to cre- 
ate an electric brush discharge. There is, of course, a strong oscil- 
latory electric field outside the helix, and vacuum tubes held there, 
particularly neon tubes, glow brilliantly. It has been contended 
that these oscillations are undamped and continuous, but I can show 
you a simple experiment with a neon tube which proves that they 
ure not always uninterrupted. If I hold a neon tube near the helix, 
wend move it rapidly to and fro, you see a broad band of hght, due 
to persistence of vision, but this is cut up by dark lines and spaces. 
In the same manner if a neon tube is rotated near the helix it does 
not produce a uniform disk of light, but the disk presents the appear- 
ance of radial dark bands and bright spaces. The same effect is 
seen with a vacuum tube filled with any other gas, provided the tube 
is sufficiently narrow in the bore. It appears to me that this proves 
incontestably that the oscillations are not uninterrupted, but are cut 
up irregularly into groups of various lengths.¢ 
To obtain these high-frequency oscillations the various contribu- 
tory factors—strength of magnetic field, length of arc, supply of coal 
gas—have to be carefully adjusted with reference to the capacity 
and inductance used and the voltage on the are. No one who has 
practically worked with the apparatus can say that it is a simple and 
easy one to use. A very little want of exact adjustment causes the 
arc to be extinguished or else it fluctuates greatly in current, and 
compared with the extremely simple appliances required for spark 
telegraphy, the advantage in ease of working is largely on the side of 
the spark. But we have to consider whether there are not counter- 
balancing advantages as a generator of telegraphic electric waves 
which make up for the increased difficulty of working and greater 
complexity of apparatus. The claim made for it is that if the trans- 
“Previous experimentalists seem to have been satisfied with examining in a 
revolving mirror the flaming are or brush produced at the secondary terminals 
of a transformer, the primary of which forms the inductance in the condenser 
circuit, and finding the image drawn out into a band of light concluded that 
the oscillations were continuous. The neon tube is a more delicate test, and 
reveals the discontinuity mentioned above. This discontinuity of the train of 
oscillations seems to depend to some degree upon a want of-perfect regularity 
in the rotation of the carbon terminal. It may also be brought about by the 
energy transferred to the condenser circuit being radiated or dissipated faster 
than it is supplied. 
