Biography (A&E, 8-9 p.m.): The real communications revolution took place -- it could be argued -- long before satellites, cellular telephones, or digital technology. It happened when a 21-year-old American first managed to transmit sound through thin air.
His name was Guglielmo Marconi, and his invention was radio, then called wireless telegraphy. ''Marconi: Whispers in the Air'' marks the 100th anniversary of the event by telling his story -- including the ridicule of fellow scientists at the absurd notion that a signal could be sent with no wires.
Photos and film clips not seen on TV before help document his career, along with a ''sound collage'' commissioned for the production.
500 Nations (CBS, 8-10 p.m.): State-of-the-art documentary techniques and big names have been marshaled for this ambitiously comprehensive documentary -- four hours over two nights -- on the history of American Indians. Three-dimensional computer graphics and high-tech matte paintings are employed, along with an array of standard material like interviews, location shots, artworks, and still photos.
Kevin Costner is host, partly because of his work as director and star in the 1990 film about Indian life ''Dances With Wolves,'' which won the Best Picture Oscar and gained Costner the award for Best Director. The show is narrated by Gregory Harrison, and some 30 well-known actors read the words of historical figures.
The program ranges from the Arctic to Central America and covers the period both before and after the arrival of Europeans. The long, complex sweep of time is viewed through Indian eyes in many cases and shows the personal meaning that myths and other cultural treasures have had for the original people of the land.
The production also applauds their resiliency and courage in the struggle for survival and identity during the sometimes devastating years since white settlement began. Part 2 airs Friday, April 21, 8-10 p.m.
Please check local listings for these programs.