RESONANCE CURVES

.129

wireless telegraphy. It consisted of a condenser of fixed capacity and
continuously variable self-inductance. A Geissler tube or a spark gap
served for frequency measurements by means of resonance, while a
bolometer was used for decrement determinations.

The next step in this direction is represented by the FRANKK-DONITZ
(Telefunken) wave meter shown in Fig. 156; it consisted of a variable
condenser, interchangeable coils for the different ranges and a hot-wiro-
air thermometer. Very similar in design and equally simple is the port-

PIG. 159.
able wave meter of the MARCONI Co., of which Fig. 157 shows the con-
nections diagrammatically, Fig. 158 the finished construction; it conHint-H
of a variable condenser, a fixed self-inductance of rectangular nhape
mounted into the cover of the case and a carborundum detector [Ai t.
160] with telephone.
The later wave meter of the TELEFUNKEN Co. (Fig. 159) whose adj UHt-
able condenser, in addition to its graduated scale, also has three seal OH
of wave-lengths corresponding to the different coils, while more compli-
cated, has a much wider range of usefulness. The same applies to tho
portable decremeter of the MARCONI Co. (Fig. 160).