32 



SCIENCE. 



(Vol. II., No. 23. 



' THE NATIONAL RAILWAY EXPOSI- 

 TION.^— II. 



The numerous accidents that have occurred 

 owing to the signals showing ' clear ' when the 

 switches were set for a side-track led to the 

 invention of 'interlocking,' which is now used 

 extensively in England, and is being intro- 

 duced into this country. The term ' interlock- 

 ing ' applies to a S3'stem where the switches 

 and signals can be so worked hy levers con- 

 centrated at one point, that no safetj^-signal 

 can be given for any track until the switches 

 are properly set for the safe passage of the 

 train ; and, when the signal is set to safet}*, 

 none of the switches can be moved until the 

 signal is again made to indicate danger. The 

 advantages of this system are, that one man 

 can operate a large number of switches and 

 signals, and the interlocking apparatus acts as 

 a check upon him, and renders it Impossible 

 for him to commit a mistake and move a wrong 

 lever ; and the mechanism is so arranged that 

 a certain deflnite routine must be gone through 

 in making a safe course for a train. The sig- 

 nals standing at their normal position of ' dan- 

 ger,' the switches are first moved, then thej^ 

 are locked firmly in position : then only can 

 the danger-signal be changed to safety for the 

 passage of the train when all possible confiict- 

 ing signals or switches are locked, so that they 

 cannot be operated. When a certain track has 

 been prepared for the safe passage of a train, 

 the necessarj' alteration of switches and signals 

 is begun at the point farthest from the train, 

 and ended at the signal nearest to it, this signal 

 being locked to indicate danger until the track 

 is ready for the train ; and the setting of this 

 signal to safety shall lock to danger all conflict- 

 ing signals not alreadj^ locked. 



The amount of safety secured by the adop- 

 tion of interlocking apparatus is thus laid down 

 b}' an English author : " If a man were to go 

 blindfold into a signal-box with an interlock- 

 ing apparatus, he might, as far as accordance 

 between points and signals is concerned, be 

 allowed with safety to pull over any lever at 

 random. He might doubtless delay the traffic, 

 because he would not know which signal to 

 lower for a particular train ; but he could not 

 lower such a signal, nor produce such a combi- 

 nation of position of points (switches) and 

 signals, as would, if the signals were obeyed, 

 produce a collision." 



Interlocking has been verj- generally adopted 

 in England, but hitherto little attention has 

 been paid to the subject in this country' ; though 



1 ContiQued from No. 22. 



in some crowded depots, such as Lowell, Wil- 

 mington (Del.), and Boston (Boston and Al- 

 banj- railroad), it has recentlj" been introduced 

 with great success. 



The two principal exhibits of interlocking 

 and signalling apparatus at the Chicago exposi- 

 tion are those of the Pennsylvania steel com- 

 pany and the Union switch and signal company ; 

 Mr. George Westinghouse, so well known as 

 the inventor of the break bearing his name, 

 being the president of the latter company. 

 The Union switch and signal company exhibits 

 several distinct methods of working switches 

 and signals controlled bj- interlocking appara- 

 tus. First, the Saxbj' and Farmer method, 

 which is very generally used in England, and 

 in some station-j-ards on the continent ; Brus- 

 sels, for example. In this the whole work of 

 moving the signals and switches is effected by 

 the manual power of the signalman. But as 

 this involves considerable physical exertion in 

 places where the levers are numerous, and some 

 of the signals are a considerable distance awaj', 

 Mr. Westinghouse has introduced a sj'stem 

 whereb}' the signalman onlj' moves valves ad- 

 mitting either compressed air, or a mixture of 

 water and wood, or methylated spirits of wine, 

 to cylinders, the pistons of which perform the 

 actual hard work of shifting the switches and 

 signals. The Peunsj'lvania steel company 

 shows an American invention, which proceeds 

 on similar lines to the Saxby and Farmer ap- 

 paratus, attaining, however, the same end by 

 the use of fewer levers. As, therefore, these 

 two sj'stems are verj' similar, except as re- 

 gards mechanical details, into which we need 

 not enter here, the following descriptioYi of 

 the general methods and purposes of interlock- 

 ing mechanism will apply to both exhibits. 

 The whole question is novel on this side of the 

 water, and will well repa^' a careful study by 

 all those who are interested in the progress of 

 railroads. 



One of the points that has been equipped 

 with interlocking apparatus by the Pennsyl- 

 vania steel company is shown in the accom- 

 panying plan of tracks at the Union Junction 

 of the Philadelphia, Wilmington, and Balti- 

 more railroad, at Wilmington, Del. This 

 junction is one mile west of the passenger- 

 station, at the crossing (at grade) of the Wil- 

 mington and northern railroad and of the 

 Delaware western railroad, where the Dela- 

 ware railroad branches from the main line of 

 the Philadelphia, Wilmington, and Baltimore 

 railroad. Through trains pass this junction 

 at lightning express speed. The main line 

 is protected from crossing roads b}- dead 



