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Tone
Tenor
The highest male singing range. The next highest is alto. (See also: Bass and Treble.)
Timbre
The quality, or ‘colour’, of a sound. It depends on the number of overtones and how loud each overtone is compared with the others.
Tone
A simple tone is a pure note,
such as middle C. It is produced, for example, by a certain vibration of a string or in the pipe of
a wind instrument. However, the pure tone would sound quite dull and have little of the richness that we normally expect.
The richness is produced when
the pure tone, which is called the fundamental tone, is accompanied by a number of other tones that are multiples of the fundamental. They are called overtones. If they are exact multiples of the tone, they are called harmonics. The fundamental tone, accompanied by its overtones, makes a pleasant sound and is distinguished from the pure tone by being called a musical tone.
The reflecting telescope was developed by Herschel at the end of the 18th century. In 1781 he discovered the planet Uranus using a mirror telescope. The world’s largest telescopes are all mirror telescopes.
A combination of mirror and lens was developed in 1930 by Schmidt. It uses a weak ‘correcting’ lens in front of a curved mirror. It gives a wide field of view that is useful for looking at the whole sky.
(See also: Absorption of light; Light-gathering power; Resolving power.)
Telescope barrel
Objective lens
Incoming parallel rays from distant object
Plane mirror
Concave mirror
 Telescope – The principle of a mirror telescope. Light from a distant object produces parallel rays that are reflected by the main mirror. The light rays converge and are reflected by a small plain mirror to the side of the telescope, where they are focused by an objective lens.
Objective lens in eyepiece
Telescope barrel
Vertical adjustment
Horizontal adjustment
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