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. [Illustration: FIG. 4. [Illustration: FIG. 5. SIX-INCH PNEUMATIC TUBES IN PROCESS OF BORING AT THE SHOP OF A. FALKENAU, PHILADELPHIA, PA.] =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