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The Telephone 163 age diameter of the cable is a little less than 3 inches. In this underground trunk road approximately 1,375 tons of copper wire have been used. During the trials with this underground cable some interesting achievements were recorded. At the transmitter in the General Post Office in London a person spoke and his words travelled to Birming- ham and back, being received in another room in the General Post Office. Thus the voice travelled a distance representing a continuous line of 221 miles. Then four of the first layer circuits were coupled up and spoken through, the words travelling from London to Birmingham, back again to London, thence a second time to Birmingham and once more back to London, representing 542 route miles. Two additional loops, representing the central core, were now coupled in so that the voice had to travel three times to Birmingham and back, representing 663 miles. This distance coincided practically with a length of underground cable reaching from London to Aberdeen, and the results were considered to be completely satisfactory. As a final test two more loops of the first layer were brought in, causing the voice to make four round trips between the trans- mitter and receiver, the distance this time being equal to 884 miles of continuous cable, or approxi- mately the distance between New York and Chicago. While speech over this reach was possible it was not considered commercially satisfactory. At the time this test was carried out it represented the longest distance over which conversation had been main- tained with underground cables. Although the telephone has made remarkable