Sonar waves help us to ‘see’ by using sound. A sonar device fitted on a ship sends out sound waves that travel through water. When these
sound waves strike an object, they are reflected back. The reflected waves are received by the ship, and can be used to ‘draw’ an image of the object and its location on a computer screen.Did you know that the word SONAR stands for Sound Navigation and Ranging?
Morse code was a system of signaling in which letters and numbers were sent as short electrical signals which formed dots and long electrical 
signals which formed dashes.The Morse code was invented by Samuel F.B. Morse, a painter and founder of the National Academy of Design. He conceived the basic idea of an electromagnetic telegraph in 1832, and produced the first working telegraph set in 1836. This made transmission possible over any distance. The first Morse Code message, ‘What hath God wrought?’, was sent from Washington to Baltimore.
What will television of the future be like? It is quite possible that screens will grow larger and larger even as they grow thinner and thinner. 
TV sets will have liquid crystal displays like the screens of a hand held computer game. At the same time there will a stunning increase in the number of televisions per household, as small TV displays are added to clocks, and maybe even coffee cups! Who knows… television may even be placed inside books and, before long, books will evolve into no more than hundreds of small flat-screens stapled together!
We know that Marconi was the first person to build a machine that could produce radio waves by making a powerful electric spark. His radio
set could send messages, but the first radio broadcast occurred on Christmas Eve in 1906, and was made by Reginald Fessenden, a Canadian engineer, from Massachusetts in US. Wireless operators on ships at sea were the first people to hear this broadcast. They were amazed to hear a human voice coming from their instruments as someone spoke. Then a women’s voice rose in song! Many of them called their officers to come and listen, and soon, the wireless rooms were crowded. Next, someone was heard reading a poem. Then there was a violin solo… and then a man made a speech In this first broadcast, Fessenden himself played ‘Holy Night, Silent Night’ on the violin. He also read Christmas story from the Bible (Book of Luke) and played a phonograph recording of Handle’s ‘Largo’. It was truly a Christmas Eve to remember!
Phone lines are not used only for conversations. If you have a videophone, you can actually see who you are talking to, as the phone lines 
are used for faxes through which you can send pictures, photos, and letters. Computers also use phone lines for an Internet connection, with which you can browse and chat for hours!
Handling of mail often exposes postal workers to dust, especially when the mail bags are opened. Sometimes, dangerous chemicals may be split, and 
there are also electrical hazards that workers have to face. So postal systems have always been interested in mechanizing post offices. Between World War 1 and II, many postal systems introduced conveyor belts to move mail between handling points. The letter sorting office at Mount Pleasant in London was one of the most highly mechanized in the world Gradually, machines were introduced to prepare mail, and sort small letters from the bigger ones. There were also machines to stamp the date on letters and to put them neatly into sacks In modern, mechanized sorting systems, workers sit at a keyboard while letters are mechanically passed in front of them. Approximately fifty to sixty letters each minute are processed by the operator. Based upon the code entered by the operator, the letters are segregated into different bins, and then removed, bundled and dispatched by the postal workers
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