1. Microwaves: a region of the spectrum of the electromagnetic waves, in the wavelength range from about 1 mm to 300 mm, with a frequency range of 1000 MHz to 300,000 MHz. (Definitions of the frequency range vary)
Microwaves sources include tubes called Klystrons. The use of Microwaves includes radar, microwave ovens and telephone communications.

2. Mirage: an optical illusion caused by refraction in air of non-uniform temperature. It is seen when the air close to the ground is warmer than the higher up. As light nears the ground, it bends away, and an image appears on the other side of the surface.

3. Microphone: Device that converts sound waves to a changing electric current. The current may be amplified and passed to an oscilloscope, recorder or speaker. A moving coil microphone is similar to loudspeaker but works in reverse.

4. Camera: An optical instrument able to produce a permanent record of a scene by focusing light onto a light-sensitive material or device.

5. Echo: The reflection of a sound or another kind of wave from an object or surface. Echoes are joined in sound-ranging or sonar.

6. Geological Time: A time scale suitable for describing the history of the Earth since it formed thousands of millions of years ago. The time is divided into a number of ages and periods, based mainly on the life then existing on Earth.

7. Global Warming: A predicted result of the Green House Effect, in which increasing quantities of industrially produced Carbon dioxide (and other pollutant gases) in the atmosphere act as a blanket to radiation leaving the Earth. This is predicted to produce a gradual increase in the average temperature of the Earth, leading to expansion of the oceans, melting of ice claps and glaciers, and the alteration of the climatic and the weather patterns.

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