National Geographic : 1929 Jun
I 800 conversations at once through a cable less than 3 inches thick An Advertisement of the American Telephone and Telegraph Company THE earth beneath our great cities is crowded. Steam, gas, sewer and water-mains, compressed air pipes, pneumatic tube systems, telephone Ai3,.N~ is: and telegraph cables, light, power and rapid transit conduits lie so close together that any further additions create serious engineering problems. Yet the number of telephone calls that must flash through the underground arteries of great cities is steadily increasing. The challenge to the scientific minds of the Bell System was to find a way for more conversations in existing conduits. Fifteen years ago, the pride of the System was a cable containing nine hundred pairs of wires. Then by many improvements a cable of twelve hundred pairs was perfected. It was rightly considered a scientific triumph. Today, cables containing eighteen hundred pairs of wires are in service, and these cables with every wire insulated are only two and five-eighths inches in diam eter, one-half as large as the first nine hun dred-pair cable. Eighteen hundred conversa tions at once-six hundred more than before -can now pulse through this two and five eighths inches of cable. There is no standing still in the Bell System. Better and better telephone ser vice at the lowest cost is the goal. Present improvements constantly going into effect are but the foundation for the greater ser vice of the future.