With the President and the Congress tussling over the date of the transition of broadcast television from analog to digital, this may be an opportune time to reflect on the magnitude of this event.

With an estimated 6.5 million homes currently unable to receive a digital TV signal, the stakes are high. The American people will tolerate a great deal, but heaven help the politician who takes away their television.

This event — whenever it eventually happens — will be unprecedented in the history of mass media. Never before has a major broadcast infrastructure been shut down.

There have been media formats — such as Edison wax cylinders, RCA SelectaVision video discs, Laservision laser discs, and Betamax video cassettes — that have fallen by the wayside. And three years ago, on January 27, 2006, Western Union exited the telegram business. But no major consumer broadcast service has pulled the plug on its audience like the switch digital television will do. From the dawn of electronic media in the 19th century throughout its expansion in the 20th, new features have been added in an evolutionary manner compatible with what went before.

I own a candlestick telephone from circa 1915. It doesn’t have a dial — the phone is from the era in which you lifted the earpiece and toggled the hook several times to get the attention of your local operator who would then place your call. But with an RJ11 jack spliced on the end of the cord, you can plug it into the wall and it still works with today’s telephone infrastructure. When alerted by the sound of another phone in the house with a ringer — the candlestick phone as none — you can pick up the earpiece of 1915 phone and talk to anyone in the world. With practice, you can even use it to dial by rapidly toggling the earpiece hook, which is the equivalent of pulse dialing on a rotary phone.

Similarly, radios that originally received Orson Welles’ War of the Worlds broadcast and President Roosevelt’s fireside chats can still capture AM radio stations playing the latest Britney Spears pop tune.

A television manufactured in the U.S. shortly after World War II would still work today — at least up until the digital TV switch occurs. It would, of course, only display a black-and-white image of programs on channels 2 through 13. But, even today, that’s enough to watch everything from the NBC Nightly News to Lost throughout most of the U.S.

Since the 1940s, American broadcast television has introduced color, stereo sound, secondary audio programming, and closed captioning without impairing the existing functions. Think about that for a moment. Changes as radical as the transition from black-and-white to color were added to television’s broadcast signal without disrupting the previous service.

We are now on the precipice of eliminating television signals from the traditional broadcast frequencies. The electromagnetic spectrum they occupy is too valuable to leave to analog NTSC TV signals. You’ll be able to tell your grandchildren you were there the day that millions of television sets went dead, displaying nothing but random snow.

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