In 1871 a speech therapist named Alexander Graham Bell began teaching deaf pupils in Boston. He opened a school to train teachers, and began working on a device to help the deaf to hear. This resulted in the invention of the telephone which was able to transmit a message over a wire to his assistant, Thomas Watson, who was in another room. Bell received a patent on the telephone on February 14, 1876, just two hours before Elisha Gray applied for a patent on a similar device. One year later Thomas A. Edison demonstrated the first "talking machine." In Bell's telephone a sound wave caused a thin diaphragm to vibrate which produced a fluctuating electric current in a wire. This electric impulse was transmitted to a receiver where a similar diaphragm reversed the process and reproduced the original sound. Edison's invention used the same principle to activate a stylus that cut a groove in a rotating cylinder or disc, thereby creating a permanent recording of the acoustical signal.
Since these crude but historic beginnings, both inventions have been refined and technically improved. Microphones have replaced acoustic horns and are of several types. Carbon, dynamic, crystal, condenser, and ribbon microphones are all designed to convert sound waves to electric impulses. In 1940 microwaves were introduced for transcontinental transmission, and in 1956 the first transoceanic cables were laid. Today, satellites in geosynchronous orbits 25,000 miles high make worldwide communication possible.
The telephone and phonograph are complicated instruments, but they pale in comparison to the human ear. The ear is designed to convert a longitudinal sound wave in the air into a mechanical vibration in the ear drum, then in the three ossicle bones: the hammer, anvil, and stirrup, and then in the round window to produce a wave in the fluid filled cochlea; this wave causes an electrochemical impulse in the auditory nerve which is then interpreted in the auditory center of the brain as sound. Thus, a sound wave goes through several essential steps before it reaches the brain. Any interruption of this complicated process can cause serious hearing problems. Modern medical procedures can correct some of these problems with hearing aids or surgery, but damage to the auditory nerve is irreversible. Much of what occurs in the hearing process is still a mystery. We can understand the mechanical aspects of hearing, but how these mechanical vibrations are converted into electrical impulses in the delicate nerve endings of the cochlea, and how these impulses are detected and interpreted by the brain is still unknown. When we consider the intricate construction and function of the human ear, indeed we are constrained to agree with David that we are "fearfully and wonderfully made."
