Pneumatic mail tube receiver at New York City Post Office, 1897.

Photograph taken from 'Scientific American' (1897), showing a postal worker and the rear of a closed receiver. Pneumatic mail tubes (PMT) were first introduced in Philadelphia in 1893 and in New York City in 1897. They were usually eight inches in diameter and were used to carry mail in bulk between sorting offices. The system in New York covered about 27 route miles, and remained in use until 1953, by which time it was the last such system in operation.