In order to demonstrate the practicability of the system, the Electro-Pneumatic Transit Company had constructed in the basement of the Mills Building, on Broad Street, New York, a short line of small brass tubing, about two or three inches in diameter, with one branch, thus connecting three stations together. The tube was very short, probably not more than two hundred feet in length. The air-pressure required was very slight, probably not more than an ounce or two, being supplied by a small blower run by an electric motor.

At the junction of the branch and the main tube was located a switch that could be moved across the main tube and so deflect the approaching carrier into the branch. This switch was moved by an electro-magnet, or solenoid, that could be excited by pressing a button at the station from which the carrier was sent. When the carrier passed into the branch tube it set the switch back into its normal position, so that a second carrier, following the first, would pass along the main tube, unless the switch was again moved by pressing the button at the sending station.

This tube in the Mills Building worked well, but it was of a size only suited to the transmission of cash in a store or other similar service. It could not be said, because this tube worked well, that a larger and longer tube with numerous branches would work equally well. In fact, there are several reasons why such a tube would not operate satisfactorily. The method of operating the switches was impracticable. Suppose the branch tube had been located two miles away from the sending station and that it would take a carrier four minutes to travel from the sending station to the junction of the branch tube. Again, suppose that we have just despatched a carrier destined for a station on the main line beyond the junction, and that we wish to despatch the second carrier to be switched off into the branch tube, we must wait at least four minutes, until the first carrier has passed the junction, before we can press the button and set the switch for the second carrier which may be on its way. How are we to know when the first carrier has passed the junction, and when the second will arrive there, in order that we may throw the switch at the proper time? Must we hold our watch and time each carrier? It is plain that this is not practical. I take this as an illustration of the impracticability of the Clay-Lieb System as constructed in the Mills Building when extended to practical dimensions. I will not describe the mechanism and details of the system, which are ingenious, but will say in passing that the automatic sluice-gates, which work very well in a three-inch tube with carriers weighing an ounce or two and air-pressures of only a few ounces per square inch, would be useless and could not be made to operate in a six-inch tube with carriers weighing from eight to twenty-five pounds and an air-pressure of from five to twenty-five pounds per square inch. For further information the reader is referred to the patents of Clay and Lieb.

Franchises and First Government Contract.

—In the spring of 1892 an ordinance was passed by Common and Select Councils, and signed by the Mayor of the City of Philadelphia, permitting the Pneumatic Transit Company to lay pneumatic tubes in the streets of that city. At the time this franchise was granted negotiations were in progress with the post-office department, in Washington, for the construction of a six-inch pneumatic tube, connecting the East Chestnut Street sub-post-office, at Third and Chestnut Streets, with the main post-office, at Ninth and Chestnut Streets, for the transmission of mail. This sub-post-office was selected because more mail passes through it daily than any other sub-office in the city, it being located near the centre of the banking district. Negotiations were delayed by various causes, so that the contract with the government was not signed until October, 1892.

Search for Tubes.

—It was at this time that the writer was first employed by the Pneumatic Transit Company, as engineer, to superintend the construction of this line. The company commenced at once to carry out its contract with the United States government, both the post-office department and the company being very desirous of having the work completed before winter. The time was very short for such an undertaking, but wrought-iron tubes had already been ordered of a well-known firm who manufacture pipe and tubing of all kinds. After waiting four or five weeks the first lot of tubes were finished, but upon inspection it was found that they were not sufficiently accurate and smooth on the interior to permit of their being used for the purpose intended. The next thing that suggested itself was seamless drawn brass tubes. While they would be very expensive, the process of manufacture makes them eminently suited for the purpose, but they could not be obtained in time. A city ordinance prohibits the opening of the streets of Philadelphia during the winter months except in extreme cases. Accurate tubes must be had, and had quickly. It then occurred to the writer that it might be possible to bore a sufficient quantity of ordinary cast-iron water-pipe and fit the ends accurately together to answer our purpose. Inquiry was made at nearly all the machine-shops in the city, to ascertain how many boring-machines could be put upon this work of boring nearly six thousand feet of six-inch pipe. It was found impossible to get the work done in time, if it was to be done in the usual manner of boring with a rigid bar. At last a man was found in Mr. A. Falkenau, engineer and machinist, who was prepared to contract for the construction of twelve special boring-machines and to bore all the tubing required. Suffice it to say, that the machines were built, and about six thousand feet of tubes were bored, between November 8 and December 31.

Fig. 6.
PIPE BORING APPARATUS.

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