RADIOTELEGRAPHY—FLEMING, ihrer 4 
than in the opposite direction (see fig. 16). The result of these 
experiments was also to show that the current voltage curve or 
characteristic curve of a carborundum crystal is not linear—that is to 
say, the crystal as a conductor does not comply with Ohm’s law, for 
the resistance of the crystal decreases as the current is increased. 
Hence the conductivity of the crystal is a function of the voltage 
acting on it (see fig. 16a). 
Accordingly, if we pass a 
current from a local cell 
through a crystal under a 
voltage say of 2 volts, a 
telephone being inserted in 
series with the cell, and if 
we apply an_ oscillatory 
voltage also to the crystal, 
which varies say between 
+0.5 and —0.5 volt, then Applied Voltage. + 
the crystal 1s alternately Fic. 16.—Characteristic curves of carborundum 
subjected to a voltage of 2.5 crystal. 
and 1.5 volts, but the corresponding currents would be say 8.4 and 
1.8 microamperes, as shown by an experiment with one particular 
crystal employed by Professor Pierce. The mean current would then 
be 5.1 microamperes, whereas the steady voltage of 2 volts would 
only pass a current of 4 microamperes. Hence, apart from the uni- 
lateral conductivity, and merely in virtue of the fact that the char- 
acteristic curve is not a straight line, we find that such a crystal or 
even a confused mass of crystals 
can act as a radiotelegraphic de- 
tector. There are, therefore, two 
ways in which a crystalline mass 
of carborundum can be used as a 
radiotelegraphic detector. It con- 
sists of a conglomeration of crys- 
tals arranged in a_ disorderly 
manner, or not so symmetrically 
as to neutralize one another’s uni- 
Applied Voltage. lateral conductivity. Hence the 
a as mass of crystals, like the single 
crystal, possesses unilateral conductivity, and also a conductivity which 
is a function of the voltage applied to it. We may then use it without 
a local cel’, and avail ourselves of its valve property to rectify the trains 
of oscillations in the antenna and convert them into short unidirec- 
tional trains which can affect a galvanometer or telephone; or secondly, 
we may place the crystal between the ends of a circuit containing a 
telephone and a shunted voltaic cell, and then on passing oscillations 
Current. 
