VOt. XLIV.l PHILOSOPHICAL TEANSACTIONS. 183 



drain marshy grounds, or other useful purposes, where no head of water can be 

 procured, and the current runs very slowly : circumstances which render most 

 other engines useless. 



The axis of the first mover is cut into the form of an hexangular prism, of 

 dimensions suitable to the force required, as is represented by the letter a, fig. 

 2, pi. 4. Into this, several sets of holes are mortised, as bbb. These are in- 

 tended to receive different sets of sails made of iron plates, one of which is repre- 

 sented at c ; all which sails are weathered in the same manner as those designed 

 for windmills ; only in these, the extremity of their ends stands parallel to the 

 planes of each end of the axis ; viz. those ends which are farthest from the centre 

 This hexangular axis, when employed, must be placed parallel to the moving 

 stream, and may lie even with its surface : but the engine will act most vigor- 

 ously, when it and all the sails employed are entirely under water, as is easy to 

 comprehend. 



Each set of the sails before described contains 6 in number, and are so con- 

 trived as to be put in and taken out at pleasure. Whence it follows, that when 

 a single set of sails is made use of, the engine produces a single effect ; when 3 

 sets, a double ; and so on, till the desired momentum is acquired, with the same 

 quantity of running water, provided there be room to fix a sufficient number of 

 sails. 



It is further to be observed, that when this engine is placed with its sails, made 

 and weathered as above directed, they will move with equal velocity, even sup- 

 posing the current should change its course, and come upon them in a quite con 

 trary direction ; as the case really happens in rivers where the tide ebbs and flows ; 

 where most other engines yet invented are of little use. 



About 6 weeks ago a model of this engine was tried. It was fixed in our 

 river, in a place where the water moved only 1^ feet in 20 seconds ; in which 

 time the first mover made 6 revolutions. Its diameter was no more than 2 feet 

 2 inches ; yet it would have lifted 14 pounds 2 yards high in the above-mentioned 

 time, had not a misfortune happened to its case, which made it not perform 

 quite so much. 



It appeared somewhat extraordinary, that the circumference of its first mover, 

 viz. any determined part of it, passed through a space of 42 feet in 20 seconds ; 

 which is nearly twice as fast as the motion of the water : and as the momentum 

 will be in proportion to the number of the sets of sails that are employed, its 

 force is capable of being greatly augmented with the same quantity of water : a 

 thing not to be admitted without sufficient experiment, but what seems ex- 

 tremely plain in theory, and what probably will answer when brought to practice. 



This engine, when once seen, requires little skill for constructing it, is made 

 at a small expence, and easily kept in repair. 



