SELF-CLOSING DOOR 



161 



from the point, "B," to a pulley, "D," thence to a counterpoise 

 weight. 



Whichever way the door is opened the cross-piece pulls on the 

 bridle, one end of which draws tight as the other end loosens, 

 which in turn lifts the weight. As soon as the door is released a 

 corresponding strain is placed on the bridle by the weight, which 

 closes the door. 



Fig. 112. — Details of a self-closing door. 



It is more complicated to describe this device than to build it. 

 The essential idea is to have the weight evenly distributed on 

 both sides of the cross-piece, which really amounts to having the 

 cross-piece and bridle of the same length on both sides of the door. 

 Thus, when the weight is distributed, and the door remains at 

 what we might call a dead center, it will be in a closed position. 



The size of the counterpoise will necessarily depend upon the 



