National Geographic : 1947 Mar
Birthplace of Telephone Magic 1,500,000 Vacuum Tubes, from Peanut to Coffee-urn Size, Work in the Telephone System Two largest "overseas" tubes boost the voice across oceans. Overland amplifiers send the voice across country. Power plant tubes charge batteries. Magnetron tube on black base in radar group was a "secret weapon." O National Geograiplic Society ktal iromes by \illard It. ('ulver For Best Results, Hold Your Telephone Close to Your Lips The telephone's ability to pick up speech at various distances from the mouth is tested in a soundproof room. A loud-speaker inside the dummy head emits typical human words and sounds.