2.  As early as the 500's B.C., A Greek philosopher and mathematician named Pythagoras invented the sonometer, an instrument used to study musical sounds.

3.  About 400 B.C., a Greek scholar named Archytas stated that sound is produced by the motion of one object striking another. About 50 years later, the Greek philosopher Aristotle suggested that sound is carried to our ears by the movement of air.

4.  The understanding that sound travels in the form of waves may have originated with the Italian artist Leonardo da Vinci about 1500. But European scientists did not begin extensive experiments on the nature of sound until the early 1600's.

5.  About that time, the Italian astronomer ang physicist Galileo demonstrated that the frequency of sound wayes determines pitch. Galileo scraped a chisel across a brass plate, producing a screech. He then related the spacing of the grooves made by the chisel to the pitch of the screech.

6.  About 1640, Marin Mersenne, a French mathematician, obtained the first measurement of the speed of sound in air. 20 years later, the Irish chemist and physicist Robert Boyle demonstrated that sound waves must travel in a medium.

7.  Boyle showed that a ringing bell could not be heard if placed in a jar from which as much air had been removed as possible. During the late 1600's, the English scientist Sir Isaac Newton formulated almost correct relationship between the speed of sound in a medium and the density an compressibility of the medium.

8.  In the mid- 1700's, Daniel Bernoulli, a Swiss mathematician and physicist, explained that a string could vibrate at mosre that one frequency at the same time. In the early 1800's, aFrench mathematician named Jean Baptiste Fourier developed a mathematical technique that could be used to break down complex sound waves into the pure tones that make them up.

9.  Acoustical research of the 1970's included the study of new uses of ultrasound, and the development of better ultrasonic equipment. During the 1980's, research included the design of better sound reproducing- equipment and the development of computers that can understand and reproduce speech.

10.  The science of acoustics deals with sound and its effects on people. A major field of acoustics is environmental acoustics, whcich involves control of noise pollution.

11.  Acoustical engineers also studied possible uses of infared - that is, sound with frequencies below the range of human hearing.

12.  People exposed to loud noise for long periods may suffer temporary or permanent loss of hearing. Lound sounds of short duration, such as the noise of a gunshot or a firecracker, can also damage the ear. Constant noise - even if it is not extremely loud - can cause fatigue, headaches, hearing loss, irritability, nausea, and tension.

13.  Acoustics involve providing good conditions for producing and listening to speech and music in such places as auditoriums and concert hall. For example, acoustical engineers work to control reverberation—the bouncing back and forth of sound against the ceiling, walls, floor, and other surfaces of the auditorium or hall.

14.  Sound has many uses in science and industry. Geophysicists often use sound in exploring for minerals and petroleum. A device called sonar uses sound waves to detect underwater objects. Warships can locate enemy submarines with sonar. Fishing boats use sonar systms to detect schools of fish.

15.  Sound with frequencies above the range of human haring is called ultrasound. It is used to clean watches and other delicate instruments.  Scientists and engineers have developed several devices for recording and reproducing sound.