produced by a Fluid in Motion. 103 



established which convey particles of water to it ; and the latter 

 are removed from the vessel, in virtue of their cohesion to the 

 water of the jet, from which they receive a direct communica- 

 tion of motion. The jet escaping in air rises to a height of, say, 

 a metre j but when it escapes beneath a water-surface it rises 

 only to one-third or one-fourth of that height, because it has 

 given up a great deal of its motion to the particles of water 

 which leave the vessel in company with it. 



The action of the so-called " hydraulic belt " is perfectly ana- 

 logous to that of a jet escaping upwards from beneath a water- 

 surface ; indeed the revolving band may be viewed as such an 

 ascending jet. The hydraulic belt is employed to raise water 

 from deep wells, and consists of an endless band of felt passing 

 over two rollers, one placed at the top and the other at the bot- 

 tom of the well ; rapid motion is communicated to the band by 

 the revolution of the upper roller, and water adheres to it, and 

 rises with it until in passing over the upper roller it is thrown 

 off at a tangent. Now water is forcibly dragged from the well 

 in virtue of its adhesion to the band ; currents are thus established 

 in the mass of liquid in the well at right angles to the direction 

 of the issuing water, and by these water is perpetually conveyed 

 to the band. The adhering particles of water share the motion 

 of the band ; and they do not descend, because, although gravity 

 could readily overcome their adhesion, it has in this instance to 

 stop a certain amount of motion associated with each particle, 

 before it can begin to act against their adhesive force. The 

 quantity of liquid raised by such a process depends upon the 

 velocity of the band and the viscosity of the liquid (which is only 

 another term for expressing the amount of cohesion possessed 

 by its particles). Thus, the rate of revolution of the band 

 being constant, if we take ether, water, and treacle as the liquids, 

 we should be able to raise a larger quantity of treacle than of 

 water, and of water than of ether • or, again, to raise equal quan- 

 tities of these liquids, we should require the band to be driven 

 with the greatest velocity for ether, less for water, and least for 

 treacle. But, on the other hand, the denser the liquid, the greater 

 would be the amount of force necessary to produce a given rate 

 of revolution. 



2. Amount of lateral action exercised by (a) a jet of water, and 

 (/3) a jet of steam of known pressure. 



a. Water -jet. — In order to gain some idea of the amount of 

 liquid entering a current laterally, I took a graduated tube (A, 

 fig. 4) 15 millims. in diameter, filled it with water, and placed 

 within it a tube B, 4*5 millims. in diameter, and drawn out at C 

 to an orifice 1*5 millim. in diameter. B was '5 metre long; and 



