2 A PERFECT FLUID. 



or to produce a separation of their particles. If a solid be 

 reduced to the finest powder, still each grain of the powder 

 is a solid hody, and its particles are held together in a de- 

 terminate shape. 



Fluids are bodies, the position of whose particles in ref- 

 erence to one another is changed by the smallest force. 

 The distinguishing property of a fluid is the perfect facil- 

 ity with which its particles move among one another, and 

 as a consequence its readiness to change its form under the 

 influence of the slightest effort. 



Fluids are of two kinds, liquids and gases. In a liquid 

 there is a perceptible cohesion among its particles ; but in 

 a gas the particles mutually repel one another. Every solid 

 body possesses a peculiar form of its own, and a definite 

 \<>lume; liquids have only a definite volume, but no pecu- 

 liar form ; and gases have neither one nor the other. If a 

 liq it id, such as water, be poured into a tumbler, it will lie 

 at the bottom, and will be separated by a distinct surface 

 from the air above it; but if ever so small a quantity of gas 

 be introduced into an empty and closed vessel, it will im- 

 mediately expand so as to fill the whole vessel, and will 

 exert some amount of pressure upon the interior surface. 



3. A Perfect Fluid Fluids differ from each other in 

 tli- degree of cohesion of their particles, and the facility 

 with which they will yield to the action of a force. Many 

 ln..lies \\liieli are met with in nature, such as water, mer- 

 cury, air, etc., possess the properties of fluids in an eminent 

 degree, while others, such as oil, tallow, the sirups, etc., 

 s.s a less degree of fluidity. The former are called 

 perfect Jluidx, and the latter viscous or imperfect fluid*. 

 In this work, only perfect fluids will be considered. 



. / ficrfi'ct /I ii ill 'IK an agrr<J(ttinn- of jxirth-lcx irhich 

 /////// nt mire, to the fdightest' i-jj'nrt mode tn 

 ill rui from one another. 





