Fig. 3 illustrates a similar arrangement, but it is to be understood that the cores about which the windings are carried in this case are of soft iron and not of hard magnetized steel.  The necessary magnetism which constantly enables the cores to exert a pull upon the diaphragm is provided by the battery which is inserted serially in the line.  Such an arrangement in action differs in no particular from that of Fig. 2, for the reason that it matters not at all whether the magnetism of the core be produced by electromagnetic or by permanently magnetic conditions.  The arrangement of Fig. 3 is a fundamental counterpart of the original telephone of Professor Bell, and it is of particular interest in the present stage of the art for the reason that a tendency lately is shown to revert to the early type, abandoning the use of the permanent magnet.

The modifications which have been made in the original magneto telephone, practically as shown in Fig. 2, have been many.  Thirty-five years’ experimentation upon and daily use of the instrument has resulted in its refinement to a point where it is a most successful receiver and a most unsuccessful transmitter.  Its use for the latter purpose may be said to be nothing.  As a receiver, it is not only wholly satisfactory for commercial use in its regular function, but it is, in addition, one of the most sensitive electrical detecting devices known to the art.

Loose Contact Principle.  Early experimenters upon Bell’s device, all using in their first work the arrangement utilizing current from a battery in series with the line, noticed that sound was given out by disturbing loose contacts in the line circuit.  This observation led to the arrangement of circuits in such a way that some imperfect contacts could be shaken by means of the diaphragm, and the resistance of the line circuit varied in this manner.  An early and interesting form of such imperfect contact transmitter device consisted merely of metal conductors laid loosely in contact.  A simple example is that of three wire nails, the third lying across the other two, the two loose contacts thus formed being arranged in series with a battery, the line, and the receiving instrument.  Such a device when slightly jarred, by the voice or other means, causes abrupt variation in the resistance of the line, and will transmit speech.

Early Conceptions.  The conception of the possibility and desirability of transmitting speech by electricity may have occurred to many, long prior to its accomplishment.  It is certain that one person, at least, had a clear idea of the general problem.  In 1854, Charles Bourseul, a Frenchman, wrote:  “I have asked myself, for example, if the spoken word itself could not be transmitted by electricity; in a word, if what was spoken in Vienna might not be heard in Paris?  The thing is practicable in this way: 

[Illustration:  Fig. 4.  Reis Transmitter]