100 Rrof. \V . Siemens on Telephony. 



attraction between the iron membrane and the wire-coiled 

 magnet-pole without bringing the former out of its position of 

 equilibrium, by bringing it between the poles of a powerful 

 horse-shoe magnet. 



The pole which was above the iron plate had the shape of 

 a ring, the opening of which formed the sound-hole, while the 

 lower pole of the horse-shoe supported the iron pin with a wire 

 coil opposite to the centre of the sound-aperture. The mem- 

 brane itself consisted of iron only in the middle, as far as it 

 was opposite to the ring-shaped pole, while the other portion 

 was made of sheet-brass, to which the iron was soldered. 

 Through the action of the magnetic iron ring the middle of 

 the iron plate became itself strongly magnetic ; consequently 

 there was a very much strengthened attraction between it and 

 the magnetic iron pin placed opposite to it, while the iron 

 plate, attracted with equal force on both sides, remained, with 

 the whole membrane, in the position of equilibrium, and could 

 therefore vibrate freely towards both sides. 



Another modification consisted in making both poles of the 

 magnet ring-shaped, and providing them with short notched 

 iron tubes wrapped round with spirals. There were now 

 exactly opposite to the iron plate two ring-shaped magnet- 

 poles of the same kind, while itself possessed the opposite 

 polarity. This is the combination I often employ with good 

 results in so-called polarized relays, in which the movable, 

 powerfully magnetized iron tongue is situated between two 

 oppositely magnetic poles of a magnet, at equal distance from 

 each, of which the ends are provided with coils. 



This arrangement has also been approved for telephonic 

 call-signal apparatus. If a point in the rim of a steel bell, 

 attached to one pole of a horse-shoe magnet, is between two 

 iron pins furnished with coils, which form the other pole of 

 the horse-shoe, a second bell, of the same pitch and with the 

 same arrangement, repeats with surprising force the sound of 

 every stroke made upon the other, if the coils of both are in- 

 cluded in a conduction-circuit. The effect is the same with 

 tuning-forks in unison. 



Instead of two bells or tuning-forks, it is sufficient to insert 

 only one in the telephone-circuit, if the question is only the 

 conveyance of the sound of the bell as an alarm-signal. Tele- 

 phones then give loud-sounding strokes of a bell. 



If in this way the capabilities of the telephone can be con- 

 siderably heightened, yet, in retaining Bell's iron membrane, 

 we are restricted within rather narrow limits, both as regards 

 the size of the membrane for receiving the sound and the 

 strength of the effective magnetism, an excess of which ren- 



