14 is a photograph of nine different vowel sounds which have caused the oscillograph to take their pictures.  They are copies of records made by Mr. Bela Gati, assisted by Mr. Tolnai.  The measuring instrument consisted of an oscillograph of the type described, the transmitter being of the carbon type actuated by a 2-volt battery.  The primary current was transformed by an induction coil of the ordinary type and the transformed current was sent through a non-inductive resistance of 3,000 ohms.  No condensers were placed in the circuit.  It will be seen that the integral values of the curves, starting from zero, are variable.  The positive and the negative portions of the curves are not equal, so that the solution of the individual harmonic motion is difficult and laborious.

These photographs point out several facts very clearly.  One is that the alternations of currents in the telephone line, like the motions of the molecules of air of the original sound, are highly complex and are not, as musical tones are, regular recurrences of equal vibrations.  They show also that any vowel sound may be considered to be a regular recurrence of certain groups of vibrations of different amplitudes and of different frequencies.

CHAPTER III

ELECTRICAL SIGNALS

Electric calls or signals are of two kinds:  audible and visible.

[Illustration:  Fig. 15.  Telegraph Sounder and Key]

[Illustration:  Fig. 16.  Vibrating Bell]

Audible Signals. Telegraph Sounder. The earliest electric signal was an audible one, being the telegraph sounder, or the Morse register considered apart from its registering function.  Each telegraph sounder serves as an audible electric signal and is capable of signifying more than that the call is being made.  Such a signal is operated by the making and breaking of current from a battery.  An arrangement of this kind is shown in Fig. 15, in which pressure upon the key causes the current from the battery to energize the sounder and give one sharp audible rap of the lever upon the striking post.

Vibrating Bell.  The vibrating bell, so widely used as a door bell, is a device consequent to the telegraph.  Its action is to give a series of blows on its gong when its key or push button closes the battery circuit.  At the risk of describing a trite though not trivial thing, it may be said that when the contact 1 of Fig. 16 is closed, current from the battery energizes the armature 2, causing the latter to strike a blow on the gong and to break the line circuit as well, by opening the contact back of the armature.  So de-energized, the armature falls back and the cycle is repeated until the button contact is released.  A comparison of this action with that of the polarized ringer (to be described later) will be found of interest.

[Illustration:  Fig. 17.  Elemental Magneto-Generator]