Existing comment:
The Weight Pit:
The rope, whether hemp or iron, would stretch with age. An arrangement of weights, sheaves, and a wheeled cart compensated for the lengthening rope. At the lower end of the incline a similar sort of arrangement compensated for seasonal expansion and contraction of the rope.
"A cast iron sheave, nine feet several inches in diameter ... is fixed on a movable carriage between the vertical wheels and the commencement of the descent of the plane... The movable carriage may be drawn backwards and forwards about fifteen feet, but it is intended generally to be kept at the end of the pit nearest to the inclined plane, by a weight connected with it by a chain. The weight is suspended in a well; the chain with which it is connected with the carriages passes over a small sheave at the top of the well, which allows it to ascend and descend as the carriage is drawn backward and forward."
-- Sylvester Welch, Report on the Allegheny Portage Railroad, 1833
The horizontal sheave and weights keep tension on the rope that raises and lowers the cars.
At the lower end of the plane, in conjunction with the hitching shed, a sheave and carriage arrangement permitted the slack in the rope caused by its expansion and contraction to be adjusted.
"The short distance which this sheave and carriage is permitted to move would not be a sufficient allowance for the contraction and expansion of the rope, but the sheave at the foot of the plane, around which the rope passes, is also placed in a carriage fixed upon ways, and can be moved backwards and forwards upward of fifty feet."
-- Sylvester Welch, Report on the Allegheny Portage Railroad, 1833 |