HOW BLOCK SIGNALS WORK Operation of Ingenious System Thai Insures the Safety of Railroad Passenger*. Comparatively few people know just what is meant by block signals when they read that a railroad has es tablished the system on its lines. The block is a length of track which, on double track roads, has at its en trance a post and movable arm, and on single track lines one at each end. To say that a 'lne has every inch protected by this system means that the entire line is divided into consec utive blocks. Only one line from Chi cago to New York is thus protected, and of the total in the United States, one-third is on the Union and South ern Pacific. The operation of the block system is simple but absolute. In a few words, it means that a train cannot move from one block into the next until the latter block is empty. As a train moves forward, the signal arm is set to show that the block just left may be entered by the next train t'ollowirir. When a train enters a block it so affects the en ergy that is a part of sig naling that the sema phore arm remains hori- A 1 ill' if zontal until the block is vacated, when the arm automatically drops and points diagonally toward the ground. Therefore, as long as the engineer sees only drooping sig nals he can keep on go ing, but the instant he finds the arm stretching out over the track, he must come to a stop, knowing that that block is occupied by another train. The energy mentioned above is elec tricity; the current being obtained from a battery near each post. The rails of each block are made as if all of one ! i we by connecting the joints with wire. The extreme ends are then connected and thus a circi is formed in which the current flows. When no train is in the block, the mechanism operated by the current pulls the arm down and holds it there. When a train enters the block the wheels and nxles, combined with the rails, form a shorter circuit, the energy that held the arm down is withdrawn and up it swings to a horizontal position. ' Each block is independent of all other blocks. When the last wheels of a train leave it, the current re sumes its flow and the signal arm at the entrance is pulled down to the "proceed" position. But before the hind wheels have finished doing this, the front wheels of the locomotive have entered the next block and caused the arm there to rise to the "stop." For a single track line the auto matic arrangement is the same, but there is a signal at each end of the block. To prevent two trains on a single track line entering a block at the same time from opposite ends, be fore the entrance to a single track block is reached the train sets a stop signal at the far end of that block, and as it enters it sets the entrance signal to stop just as is done on double track. Half a mile or more before reaching the entrance signal of each block the engineer comes to what is called the "distant," which tells him how the other or "home" signal is set. As the automatic signal is con structed, it cannot show "go ahead" unless the entire combination of rails, wire, current, magnet, etc., is work ing perfectly. If a wire parts, a rail breaks, a battery fails,a switch point \ opens the slightest, the combinatior fails and the r« leased arm re Vt.?\ sumes the horl- 'jV \ zontal position. So, T K \ when ihe engineer \ \ sees i lie stop sig- I \ \ nal, ho knows that j there may be a | j train on the block, I j 1 M an opt n switch, or a broken rail or signaling appa- jj, ratus. At night colored lights are display ed on the same posts. The lamps will burn eight days without replen ishing, but are refilled every four or five days. When the home signal is at stop, the engineer sees the flame through a red glass. The caution light on the distant is yellow. A green lights means go ahead and is used on both the home and distant signals. Where two or more lines cross at grade the general plan of semaphore arms for day and colored light for night is the same, but owing to the complications all signals are con trolled by levers operated by men from a central station. The crossing and contiguous tracks are governed by the interlocking system. When this is in perfect order and the cross ing unoccupied, it displays "stop" to every track approaching the crossing. Any change must be made by the sig nalman, and to display "proceed" he must first lock all other approaches with the stop signal. There are now about 11,000 miles of railway equipped with the block system. The only line thus protected every inch from Chicago to California Is via the Northwestern, Union and Southern Pacific. One-third of the 11,000 miles of automatic signaling is on the Harriman lines—and the North western has more miles of double track automatic than any other rail way. For the Hostess Chat on Interesting Topics