Page:The New International Encyclopædia 1st ed. v. 03.djvu/217

* BLOCK-SIGNAL SYSTEM. 187 BLOEMFONTEIN. that signal is thrown to danger by the local track circuit. As soon as his home signal goes to dan- ger, A throws his lever to its normal position of danger, thereby locking it so that the signal can- not be thrown to safety again without permis- sion from B. A drop-slide indicator or annun- ciator fomis a part of the electric mechanism, displaying through a slotted opening on the front of the instrument-ease the words "free.' 'locked.' and "train in block.' By a system of electric locking working in connection with the indicators, and operated in part by the train through track circuits, B is unable to clear A while there is a train in the block. Automatic block-signals are usually operated through the agency of electricity alone or a combination of electricity and compressed air by the passage of trains into and out of the block. A track circuit is generally used for conveying the electric current to the signals. In arranging a track circuit, a batteiy is placed at the advance end of the block. A relay and a signal are placed at the other end. Each line of rails is connected with a pole of the battery. The current passes along the rails of one side of the track, through the relay, thence along the rails of the other side of the track, thus forming a circuit. The relay controls a local circuit, which works an electro- magnet, which in the simple electric system actuates the signal, and in the electro-pneumatic system permits compressed air to operate it. Automatic block-signals are operated on two plans: (1) The 'normal safety' plan, in which the signals always show safety unless the block is obstructed; (2) the "normal danger' plan, in which the signals always show danger at all times, except when cleared by an approaching train, which can be done only when the block is clear of trains and other obstructions. When the head end of a train enters an automatic elec- tric block the current short-circuits, that is, takes the shortest path back to the battery, through the axles of the locomotive or car, and is thereby cut off from the relay, which then breaks the local circuit operating the signal. When the signal is passed by the rear end of the train it goes to danger. In the 'normal safety' plan, when the train passes out of the farther end of the block, the signal again goes to safety. In the 'normal danger' plan the currents are so arranged that the signal is set at danger until it is again cleared by an approaching train. A train-staff machine consists of an iron pillar with a vertical slot through nearly its entire length, in which is a supply of staffs. The head of the machine, called the 'locking-case.' contains the electrical apparatus for manipulating the machine. Only one staff can be withdrawn at a time from the two machines governing a block: and this only with the consent of the signalman at the receiving station, who alone controls the staffs at the sending station. Another staff can- not be removed from either machine until the one already out is restored at one or the other end of the" block. The following is the method of operation: Before starting a train from A toward B, the situation in the block is ascer- tained by means of the bell code. If the block is clear of trains and obstructions, B, when asked, unlocks A's machine. This allows A to withdraw one staff, which is given to the engineman, who, on arrival of the train at B, hands it over to the signalman there to place in his machine. As Vol. III.— 13. neither of the machines governing the block can be unlocked while the engineman has his staff, it is of course impossible to furnish a staff for an- other train until the first staff has been returned. The train-staff system is essentially a single- track system. The preceding paragraphs describe the typical methods of block-signaling, without describing the apparatus employed. This varies consider- ably, and in so many details that it canbetreated clearly only in a special treatise. The actual operation of the block system dates from Decem- ber, 18.39, when the Great Western Railway of England began telegraphing the arrival of its trains from station to station for short distances near London. The block system was introduced into the United States by the Pennsylvania Rail- road in 1876. Block-signaling is now universal in England, but it has been adopted in full or in part on only a few American railways. BLOCK TIN. An inferior variety of tin in the form of blocks. When the metal is reduced from its ores it is first poured into molds, and the ingots thus procured are heated to incipient fusion in a reverberatory furnace, when the pure tin fuses and is withdrawn; and the less pure tin which is left behind is melted at a higher temperature, poured into molds, and called block tin. See Tix. BLODG'ET, LoEix (1823-1901). An Ameri- can physicist and statistician. He was bom in Chautauqua County, X. Y. In 1851 he became assistant at the Smithsonian Institution in charge of matters relating to climate and atmos- phere. In 1857 he issued Climatology of the United States and of the Temperate Latitudes of the Sorth American Continent, a work highly praised by Humboldt. He was for several years editor of the Sorth American and secretary of the Board of Trade in Philadelphia, and had charge of the statistical work in the United States Treasury. His contributions on finance, industrial progress, and kindred subjects com- prise many volumes. BLOEMAERT, bloo'mart, Abbaham (1564- 1G51). A Dutch painter and engraver, born in Gorkum. He studied under Joost dc Beer in Utrecht, and Hieronymus Franeken in Heren- thals, and was dean of the Guild of Painters in Utrecht from 1611 to 1628. He painted biblical and mrthological scenes, flower - pieces, land- scapes, "and portraits. His works include; "Hip- pomenes Crowned in the Arena" (1626); "Old Man's Head" (1635); "Joseph's Second Dream;" and "Saint John Preaching in the Desert." BLOEMEN, blijo'men, Pieter van (called Standaert) (1657-1720). A Flemish painter, born in Antwerp. He studied under Simon van Douw; spent some time in Italy, and in 1699 was appointed dean of the Guild of Saint Luke in Antwerp. His works incluu^ "'Ruin with Cat- tle" (1710); "Halt before an Inn' (1718), and many other pictures, chiefly of military life, or landscape-. BLOEMFONTEIN, bloom'fon-tm. The capi- tal of the former Orange Free State, now the Orange River Colony, Soutli Africa, near the Modder River, 95 miles east by soutli of Kim- berley (>Iap: Orange River Colony, K 5). It is situated at an altitude of over 4450 feet, and is well built and lighted by electricity. There arc a number of fine public edifices, among which the