( 91 )



CHAP. XIII.





	PLATE VII. represents the parallel plane for such situations where height cannot be obtained; it is to extend across the river, or valley, and descends about sixty feet into each canal.



	On each end, and over the canal, a horizontal wheel is placed, to one of which is fixed the whole machinery, except the preparer and stopper, of the double-inclined plane; the chains performing the rotary movement.



	To pass the boats, one is hooked to each chain; after which., water being drawn into the tub till a power is created, the boats will rise on the plane, passing to the different ponds of the canal, and so on, in regular rotation.

	

	This is the most expeditious of all the machines: the man having little more to do than hook the boats to the chains, and draw water into the tub; the cast off hooks acting as in the double plane. In this the water to pass the boats descends to the river, or valley, and is lost in the canal; but as this plane is level, the resistance will not be great, in proportion as the length of the plane it to the depth of the pit, water will be required; but averaging situations, one ton of water will pass one of cargo: while its expense, considering the various situations and circumstances, will be about one third the sum necessary to an aqueduct. 



	But although rivers, or valleys, may be passed with ease by the three modes described, yet, in many instances, it will be advisable to construct aqueducts, particularly where there is no great difficulties to encounter; which aqueducts may be formed of iron, as in PLATE XIII. averaging the situations, much cheaper than of stone.



	But the decision on erecting of an aqueduct, or its particular construction, must depend  on a variety of circumstances; such as, the supply of water, saving of time, carriage of stone, of iron, &c. &c. adopting to the mode which will on investigation produce the greatest saving, yet answer the intended purpose.