[Illustration: FIG. 68--FIRST BELL TELEPHONE RECEIVER AND TRANSMITTER The receiver is on the left in the picture. A thin membrane of gold-beaters' skin tightly stretched and fastened with a cord can be seen on the end of the transmitter and of the receiver. An electromagnet is also shown over each membrane. This thin membrane, with a piece of soft iron attached, was used in place of the soft-iron disk of the modern receiver.] The story of Bell's struggles might seem like the repetition of the life story of many another great inventor. He knew that he had discovered something of great value to the world. He devoted his time to the perfecting of the telephone, neglecting his professional work and finally giving it up, that he might give his whole time to his invention. He was forced to endure poverty and ridicule. He was called "a crank who says he can talk through a wire." Men said his invention could never be made practical. Even after he succeeded in finding a few purchasers and some of the telephones were in actual use, people were slow to adopt it. The idea of talking at a piece of iron and hearing another piece of iron talk seemed like a kind of witchcraft. In the telephone we see another use of the electromagnet. A very thin iron disk near the poles of an electromagnet forms the telephone receiver (Fig. 69). An electric current travels over the telephone wire. If the current grows stronger, the magnet is made stronger and pulls the disk toward it. If the current grows weaker, the magnet becomes weaker and does not pull so hard on the disk. The disk then springs back from the magnet. If these changes take place rapidly the disk moves back and forth rapidly and gives out a sound. The sound of the voice at the other end of the line sets the disk in the mouthpiece vibrating. The vibrations of this disk cause the changes in the electric current flowing over the line-wire, and the changes in the electric current cause the disk of the receiver to vibrate in exactly the same way as the disk at the mouthpiece. Thus the words spoken into the mouthpiece may be heard at the receiver. [Illustration: FIG. 69--A TELEPHONE RECEIVER]