The
imperfect contact between the broken ends of the wire proved itself to
be a means of transmitting sounds, and in addition it was found to
possess a faculty which he had not anticipated--it proved to be
sensitive to very minute sounds, and was in fact a rude microphone.
Continuing his researches, he soon found that he had discovered a prin-
ciple of wide application, and that it was not necessary to confine his
experiments to wires, since any substance which conducted an electric
current would answer the purpose. All that was necessary was that the
materials employed should be in contact with each other under a slight
but definite pressure, and, for the continuance of the effects, that
the materials should not oxidise in air so as to foul the contact. For
different materials a different degree of pressure gives the best
results, and for different sounds to be transmitted a different degree
of pressure is required. Any loose, crazy unstable structure, of
conducting bodies, inserted in a telephone circuit, will act as a
microphone. Such, for example, as a glass tube filled with lead-shot or
black oxide of iron, or 'white bronze' powder under pressure; a metal
watch-chain piled in a heap. Surfaces of platinum, gold, or even iron,
pressed lightly together give excellent results.
Pages:
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324