626 PNEUMATIC DESPATCH them. In the United States, societies were formed in Philadelphia and other places. No accurate estimate of their numbers can he made, as they are without formal organization. See Est6oule, Le Plymouthisme d'autrefois et le Darbyisme d^aujourd^hui (Paris, 1858); Mrs. H. Grattan Guinness, "Answer to the Question : Who are the Plymouth Brethren ? " (Philadelphia, 1861); Edward Dennett, " The Plymouth Brethren: their Rise, Divisions, Practice, and Doctrines;" D. Macintosh, "The Special Teachings, Ecclesiastical and Doctri- nal, of the Plymouth Brethren, compiled from their own Writings, with Strictures." PNEUMATIC DESPATCH, a contrivance for send- ing packages through tubes by means of atmos- pheric pressure. The first idea of a plan for pneumatic transmission appears to be due to Denis Papin, who in 1667 presented a paper to the royal society of London on the " Dou- ble Pneumatic Pump." This consisted of two large cylinders to exhaust the air from a long metal tube containing a travelling piston, to which a carriage was attached by means of a cord. More than a century elapsed before any further effort in this direction was made. Panckouke's Dictionnaire encyclopedique des amusements des sciences (1792) gives a descrip- tion of a machine by M. Van Estin, by means of which a hollow ball holding a small pack- age was propelled by a blast of air through a tube several hundred feet in length and hav- ing many curves. This plan seems, however, to have been more an amusement than an attempt to introduce an industrial scheme. With more regard to practical results, Med- hurst, an engineer of London, published a pam- phlet on the subject in 1810. He proposed to move small carriages on rails in air-tight tubes or tunnels, by compressed air from behind, or by creating a partial vacuum in front. In 1812 he published another pamphlet, but the plan was not put into successful operation, princi- pally from insufficient means of exhaustion. About 1832 he proposed to connect the car- riage inside of such a tube with a passenger carriage running on the top of the tube ; and although the latter project has never been com- mercially successful, it was the first to be prac- tically attempted. (See PNEUMATIC RAILWAY.) More than a score of patents were taken out on the continent and in England and America, none of which met with any practical success. Eeturning to the original idea of Denis Papin, inventors attempted to accomplish pneumatic transmission by moving the load inside the tube, and in course of time achieved success. In France MM. Jarroux and Taisseau presented a project for atmospheric telegraphy before the academy of sciences, and they were suc- ceeded in the same direction by MM. Brochet and Ador. In 1857 Mr. Latimer Clark pat- ented in England his system of pneumatic transport, and in 1858 he laid down a tube in London between Moorgate street and the general post office. Several stations were con- nected by a line of tubes in which cylindri- cal carriers holding despatches were placed. The cylinders were surrounded by India-rub- ber bands to make them fit accurately, and a partial vacuum was created in front, and compressed air was also employed to act be- hind. In 1860 M. Sebillot of Paris published a scheme by M. Kieffer, his pamphlet being entitled "A Reform in the Postal Service of Paris." In England, in 1861, an iron tube, ' somewhat semi-cylindrical, about 30 in. in di- ameter and a quarter of a mile long, was laid down near Battersea, with gradients and curves like an average road. Iron carriages were made to fit the tube by means of flexible flan- ges, and a centrifugal fan moved by a steam engine constituted the exhausting apparatus. It was found that two iron carriages of about 7 cwt. each could in this way be driven at a speed of about 30 m. an hour. A pneumatic despatch company began operations in 1863. The experimental tube was removed from Bat- tersea and laid down with some additions from the Euston station of the London and North- western railway to the N. W. district post office, a distance of about a third of a mile. The packages were blown through the tube to the N. W. station by compressed air, but moved in the other direction by the excess of normal atmospheric pressure against a partial vacuum. This system has been extended to embrace sev- eral miles of tunnel about 4 ft. in diameter, besides about 13 m. of small pneumatic tubing for sending telegraph messages between vari- ous stations. The pneumatic tunnel extends from the station at Euston square to the gen- eral post office in St. Martin's-le-Grand. The central station is in Holborn, where the ma- chinery for driving the package trains is placed. The distance between Holborn and Euston square is a mile and three quarters, and that between Holborn and the post office 306 ft. less than a mile. The tubes have a horse-shoe cross section, 4 ft. 6 in. high with an area of 17 sq. ft. The straight portions are of cast iron, and the curves of brickwork faced with cement. The chief gradients in the Euston square section are 1 in 45 and 1 in 60 ; those in the post office section are 1 in 15. The car- riages weigh 22 cwt. and are 10 ft. 4 in. long, having a cross section conformable to the tube, leaving a space of about an inch all around, occupied by a flange of India rubber which causes a carriage to fit the tube in the manner of a piston. The trains are drawn from Euston square and from the post office by exhaustion, and driven to those stations by pressure. The engine is supplied by three boilers, each 30 ft. long and 6 ft. 6 in. in diameter. The experi- ments by Mr. Barlow, consulting engineer to the Midland railway company, led him to con- clude that the greatest working economy was in moving a great amount of weight at a low speed, on the high as well as the low gradients. The system can transport over the whole line, allowing for delays, an average of a ton per
