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at pleasure, without diminishing the compressure or forceof the blast, by adding another and another machine, tillall the stream is employed. It is plain, in like manner,that the fame advantage may be received from high falls,by placing one machine over another ; that after the wa-ter has performed its office in falling through one machine,it is still capable of exerting the lame action in anotherand another machine, so long as equal spaces remain for itto fall through; so that the total effect must be the fame,as if a quantity of water, sufficient for working all the ma-chines, came at first in one stream.

A fall thus divided into two machines is represented inthe middle of the annexed plate. In the lower machine,whose air-vessel is funk to a considerable depth in a pitmade in the ground, the water is forced up in the pit, onthe outside of the vessel, four feet higher than the surfaceof the water within the vessel, or of the stone on whichthe water dashes, called by the workmen the dash-board,(see page 287). The air-vessel of the upper machinehaving an additional part at one fide, which performs thefame office as the pit, the water is in like manner forcedup to the fame height in this outer part; which outervessel serving as a reservoir for the machine under it, thewater begins to act in this lower machine four feet higherup than the dash-board of the first. Whatever numberof machines the fall will admit of, the cafe is the fame inthem all : though in each of them the water falls eighteenfeet, yet as it is pressed up again four feet for the succeed-ing machine, one machine takes up but fourteen feet of thereal fall.

The outer vessel, and its communication with the air-vessel, may be conveniently formed by an upright partitionin the air-vessel itself, not reaching quite to the bottom.The outer division may be open at top, and needs not be

so