70 



GEOMETRICAL RECREATIONS 



[CH. IV 



an engine runs up one siding, such as DBA, it must come back 

 the same way. 



Initially a small block of wood, P, coloured to represent 

 a wagon, is placed at B ; a similar block, Q, is placed at G ; and 

 a longer block of wood, R, representing an engine, is placed at 

 E. The problem is to use the engine R to interchange the 

 wagons P and Q, without allowing any flying shunts. 



Another shunting puzzle, on sale in the streets in 1905, 

 under the name of the " Chifu-Chemulpo Puzzle," is made as 

 follows. A loop-line BGE connects two points B and E on a 

 railway track AF, which is supposed blocked at both ends, as 

 shown in the diagram. In the model, the track AF is 9 inches 

 long, AB=EF= If inches, and AH = FR = BG= DE=\ inch. 



H K 



On the track and loop are eight wagons, numbered succes- 

 sively 1 to 8, each ODe inch long and one-quarter of an 

 inch broad, and an engine, e, of the same dimensions. 

 Originally the wagons are on the track from A to F and in the 

 order 1, 2, 3, 4, 5, 6, 7, 8, and the engine is on the loop. The 

 construction and the initial arrangement ensure that at any one 

 time there cannot be more than eight vehicles on the track. 

 Also if eight vehicles are on it only the penultimate vehicle 

 at either end can be moved on to the loop, but if less than eight 

 are on the track then the last two vehicles at either end can be 

 moved on to the loop. If the points at each end of the loop- 

 line are clear, it will hold four, but not more than four, vehicles. 

 The object is to reverse the order of the wagons on the track, 



