Microwaves

            You might remember the heroic role that newly-invented radar .
            
            
            
             But even in its earliest years, as it was helping win the .
             war, radar proved to be more than an expert enemy locator. Radar .
             technicians, doodling away in their idle moments, found that they .
             could focus a radar beam on a marshmallow and toast it. They also .
             popped popcorn with it. .
             .
             Such was the beginning of microwave cooking. The very same .
             energy that warned the British of the German Luftwaffe invasion .
             and that policemen employ to pinch speeding motorists, is what .
             many of us now have in our kitchens. It's the same as what .
             carries long distance phone calls and cablevision. .
             .
             Hitler's army had its own version of radar, using radio .
             waves. But the trouble with radio waves is that their long .
             wavelength requires a large, cumbersome antenna to focus them .
             into a narrow radar beam. The British showed that microwaves, .
             with their short wavelength, could be focussed ina narrow beam .
             with an antenna many times smaller. This enabled them to make .
             more effective use of radar since an antenna could be carried on .
             aircraft, ships and mobile ground stations. .
             .
             This characteristic of microwaves, the efficiency with which .
             they are concentrated in a narrow beam, is one reason why they .
             can be used in cooking. You can produce a high-powered microwave .
             beam in a small oven, but you can't do the same with radio waves, .
             which are simply too long. .
             .
             Microwaves and their Use .
             .
             The idea of cooking with radiation may seem like a fairly new .
             one, but in fact it reaches back thousands of years. Ever since .
             mastering fire, man has cooked with infrared radiation, a close .
             kin of the microwave. .
             .
             Infrared rays are what give you that warm glow when you put .
             your hand near a room radiator or a hotplate or a campfire. .
             Infrared rays, flowing from the sun and striking the atmosphere, .
             make the Earth warm and habitable. In a conventional gas or .
             electric oven, infrared waves pour off the hot elements or .