256 LECTURE XXVIII. 



A piston placed in a similar manner has sometimes been made to revolve 

 continually, and to force the water through a pipe by means of a slider or A 

 spring, which intercepts its passage in any other direction. Machines of this 

 kind have been invented and rein vented, by Ramelli,* Cavalleri,f Amontons,J 

 Prince Rupert,t Dr. Hooke, Mr. Bramah, and Mr. Gwynn. Mr. Gwynn's 

 engine, which has been employed in many cases with considerable success, 

 consists of a piston or roller nearly elliptical, well fitted to the cylinder 

 within which it revolves, with a valve pressed lightly against it by a spring, 

 which causes a considerable part of the water contained in the cylinder to 

 be forced in each revolution into the pipe : the whole machine is made of 

 brass ; the spring requires very little force, for the pressure of the water 

 on the valve keeps it always close to the roller, and the friction arising 

 from this cause is even an objection to the machine. The stream, although 

 never wholly intermitted, is, however, by no means uniform in its velocity. 

 (Plate XXIII. Fig. 314... 317.) 



The pipes, through which water is raised by pumps of any kind, ought 

 to be as short and as straight as possible ; thus, if we had to raise water to 

 a height of 20 feet, and to carry it to a horizontal distance of 100 by 

 means of a forcing pump, it would be more advantageous to raise it first 

 vertically into a cistern 20 feet above the reservoir, and then to let it run 

 along horizontally, or find its level in a bent pipe, than to connect the 

 pump immediately with a single pipe carried to the place of its destination. 

 And for the same reason a sucking pump should be placed as nearly over 

 the well as possible, in order to avoid a loss of force in working it. If 

 very small pipes are used, they will much increase the resistance, by the 

 friction which they occasion. 



Water has been sometimes raised by stuffed cushions, or by oval blocks 

 of wood, connected with an endless rope, and caused by means of two 

 wheels or drums, to rise in succession in the same barrel, carrying the 

 water in a continual stream before them ; but the magnitude of the friction 

 of the cushions appears to be an objection to this method. From the re- 

 semblance of the apparatus to a string of beads, it has been called a bead 

 pump, or a paternoster work. When flat boards are united by chains, 

 and employed instead of these cushions, the machine may be denominated 

 a cellular pump ; and in this case the barrel is usually square, and placed 

 in an inclined position, but there is a considerable loss from the facility 

 with which the water runs back. The chain pump generally used in the 

 navy is a pump of this kind, with an upright barrel, through which 

 leathers, strung on a chain, are drawn in constant succession ; these pumps 

 are only employed, when a large quantity of water is to be raised, and 

 they must be worked with considerable velocity in order to produce any 



* Artificiose Machine, fol. Paris, 1588. 



t Exercit. Geomet. p. 541. Birch ; i. 285. 



J Machines et Inventions Approuvees par 1'Academie, 7 vols. 4to, 1735, v. i. 



to which work we refer for the description of numerous hydraulic machines by Per- 

 rault, Cusset, Joly, Francini, Cordamoy, Gay, L' Heureux, Joue, Martenot, Mar- 

 chand, Auger, Ublemann, Laesson, Denisart, Ledemoust, Boulogne, Saulm, Gallon, 

 Deparcieux, Gensanne, Dupuy, Amy, &c. 



Repertory of Arts, ii. 73. 



