Sundials are a device that uses the sun to tell the time. A sundial is made up of a horizontal dial plate with numbers on it, and a vertical upright called a gnomon. As the sun moves, the shadow cast by the gnomon moves around the dial plate, and you can read the time off what numbers it points to.
Some sundials use a shaft of light rather than a shadow, and the dial plate may be curved not flat. Some sundials have enough information on the dial plate to be able to tell the date as well as the time.
A telephone is a device that lets you talk to people who are a long, long way away from you - almost anywhere else in the entire world. Telephones are the most common appliance in the world.
More recently, telephones that don't need to be connected to the phone network by wires have been invented. These are called mobile phones.
A telescope is a long, tubular device that is used to look at objects that are an extremely long distance away, so far you can't even see them with your naked eye. Inside the telescope is a series of lenses that magnifies what you are looking at. Telescopes are used to look at stars and planets that are a very, very long way away.
Tis forTelevision
A television, or TV, is something you use for watching moving pictures and sound that comes from a distance. Television programs are broadcast from television transmitters, so the television signal comes into your house through cables or in the air from a tower. Your television is just the device that picks up the signal and converts it into something you can watch. You can also play games though your television. Most people today have at least one television in their house.
Tis forThermometer
A thermometer is a device that tells you how hot or cold something is. There are many different types of thermometers for different heat ranges. Some tell you how hot you are so you know if you are so sick you are running a fever. Some tell you what temperature the air is, and others tell you how hot your oven is.
The thermometer in the picture works by the expansion and contraction of mercury as the temperature changes, but most thermometers today are digital and simply display numbers.
