HYDRODYNAMICS. 



425 



let Eivieret, Paris, 1797. Mazruchelli, Idrodiaamico, 

 9 vols. PaUv. 1795. Coulomb, Experiences dettineet a de- 

 terminer la coherence dei Fluidet et let loit de leur retittance 

 dan* let momaement tret lentt, published in the Me- 

 muiret de Flnttiiul, torn. iii. p. 246. Eytelwein's Hand- 

 buck der Mechanik **d der HydraulH. Berlin, 1801. 

 An excellent abstract of this' work, by Dr Thomas 

 Young, will be found in the Journal* of the Royal In- 

 itituiion, No. I. and in Nicholson's Journal, voL iii. 



p. 25. and 79. Gregory's Mechanics, vol. i. Lond. 1806. Hutorjr. 

 Dr Thomas Young's Elements if Natural Philo- ^" * " 

 tophy, 2 vols. Lond. 1807. Mollet's Hydraulique Phy~ 

 tiqtie, Lyons, 1810. G Irani, Memoirct des Sfarans E- 

 t ranger t for 1815, and Journal des Minet PoUson, 

 Mem. de I'lnttitut, 1815. Robison's System of Mechani- 

 cal Phtlotophif, vol. ii. and iii. Art. Resistance of Fluidt, 

 Rivert, and Water.work*. 



PART I. HYDROSTATICS. 



H.nlnsta. HvDBosTATtCs, from the Greek i>*{, mater, and i 



/ stand, is that branch of the science of hydrody na- 

 mica which treats of th properties of fluids at rest It 

 comprehends the pressure and equilibrium of non-elas- 

 tic fluids, toe doctrine of specific gravities, the pheno- 

 mena of cohesion and capillary attraction, and the 

 equilibrium of floating bodies. 



De/uutions and Preliminary Obtervaliont. 



Dtfir.iiion 

 oft! 1 . .u<t. 



polarity 



wbrity 

 csruin 



tfc in- 



1 br 



AJInid is a collection of very minute material parti. 

 cles, (probably of a spherical form,) which cohere to 

 lightly to each another, that they yield to the miiallc.it 

 force, and are easily moved among one another in eve- 

 ry direction. 



Tb phenomena hibUed by fluid*, whether they 

 led b r are at rest or in motion, afford u* no reason to believe, 

 irha. that the particle* of which they are composed possess 

 phcoo- al)v polarity, or any tendency to arrange themselves in 

 * one particular manner more than another. When a 

 mat* of water is in a state of perfect equilibrium, a cer- 

 tain point of one particle i* in physical contact with a 

 cerU'.n IHMIII of another particle , but if tin- equilibrium 

 is destroyed by violent agitation, there U no ground 

 even for conjecturing, that the tame point* of the par- 

 ticles will return into contact when the equilibrium U 

 restored. The recent discoveries, however, which have 

 been made in optics, decidedly prove, that in many 

 fluids the particles assume a particular arrangement, 

 analogous to that which is exhibited in tome of the 

 crystals of the mineral kingdom, and&at they may 

 also be made to assume another arroBBjnent, simitar 

 to that which is produced in glass, &c. Ty compression 

 and dilatation. When these fluid* are inclosed in a 

 vessel, the particles uniformly affect a certain arrange- 

 ment, which is unequivocally indicated by their action 

 upon polarised light. See OPTICS and POLARISA . 



Fluids are divided into r/.u//c and tndatlic.or com- 

 prettiblt and incomnretMle fluids. The daw of elastic 

 ""* compressible fluids conits of atmospherical air, 

 and the various gaseous or aeriform bodies with which 

 chemitts have made us acquainted ; while the class of 

 inelastic or incompressible fluid* comprehend* water, 

 mercury, alcohol, and the various oil* and liquid acids. 

 The first class, in virtue of their elasticity, are rsnaMtj 

 of expanding themselves when they are unconfined, so 

 as to till any given space, or of having their bulk great- 

 ly diminished by mechanical compression;* while the 



d into 

 * " ld 



second class possess this property in such a small de- Hydrotu- 

 gree, that the diminution of their bulk by mechanical "<* 

 force is scarcely susceptible of accurate mensuration. * "Y""*' 

 The science of PNEUMATICS considers the mechanical 

 properties of the first class, and that of HYDRODYNA- 

 MICS those of the second class. 



Till within the last fifty years, it was considered as Water for- 

 an established fact, that the class of incompressible merly 

 fluids could not be reduced in bulk by the application thought in- 

 of the most powerful forces. This conclusion was de- ^"P" 1 ' 

 duced from an experiment by Lord Bacon, who filled 

 a leaden globe with water, and attempted to compress L 7 1 



it by a great external force. The fluid, however, made co 

 i'i ft i i i i menu 



its way through the pores of the metal, and stood like 



dew upon the surface of the globe. The Florentine Florentine 

 academic-Lin* repeated the same experiment with a sil- experiment. 

 ver globe, and, by violent hammering, they succeeded 

 in altering its form, and expelling the water through 

 the pores of the silver. These trials seem to have esta- 

 blished the doctrine of the incornpressibility of fluids 

 in its most strict acceptation ; but Lord Bacon deduced 

 from them the very opposite conclusion, for, after giv- 

 ing an account of the experiment which we have men- 

 tioned, he tells us, that he afterwards computed into 

 how much space the water was driven by this violent 

 prwsvre.t 



Although the experiment of the Florentine Academy Exprri- 

 ofl)i-l Ciuirnto wai cuii.iidcrcd a. decisive of tlii* |wiiiit, " "' ' 

 yet it occurred to Mr Canton, about the year 1 761 , that Ca>tOD - 

 it wa* not hostile to the idea of a small degree of com- 

 preil>ility , for the academicians were unable to de- 

 termine whether or not the water forced into the pores, 

 and through the gold, was exactly equal to the dimi- 

 nution of the internal spare by pressure. He accord- 

 ingly set about a series of experiment* on this subject, 

 g procured a small glass tube about two feet long, 

 and I \ inch in diameter, and with a ball at one end of 

 it, he filled the ball and part of the tube with mercu- 

 ry, brought the whole to the temperature of 50 of 

 Fahrenheit, and observed that the mercury stood at a 

 point exactly 6 inches above the ball. The mercury 

 wa* then raised by heat to the ton of the tube, and the 

 tube was hermetically cealed. The mercury wa* then 

 brought to the *ame degree of heat a* before, and it 

 now stood in the tube ,'.'- of an inch higher than it di<l 

 before. By performing the same experiment with wa- 

 ter exhausted of air, instead of mercury, he found that 

 the water stood in the tube ,V 5 of an inch above the 



Air I* MM U have tan rrduc*d to T1 ! TT of iu bulk in rialn'i experiment*. 



f SM B*Wi HVIr.. bj Sb.. .oL li. p. 4*1. oc th N~*m Orgtmwm, Pirt It. Sect. II. Aphorism 44. tit. Bacon Mem* to 

 hive CMMdcnd all bodies u la MOM mc**un ettic ; for, after hating einUincd what he calU the motion of liberty, and applied 

 h phenomena of leoaioa, iMMff. " that tins motion wm umcicntificalljr called by the ichooU the notion of the d<mt*taryformi i 

 lor It don not only apply to air, water, and ftamr, but to all Ibc ditcrulm of ninautent bodies, aa wood. Iron, lead, cloth, >kmi, Ac. 

 acli body hating in own measure of ejieoi or diowaaton, from wbeaet U ii with difficulty tUctchod to soy considerable diiUnce." 

 acott'a W*ftu, TO), ii. p. Ml. Aph. M. . 



VOL. XI. rRT II. 3 H 



