584 



• KNOWLEDGE • 



[Apbil 21, 1882. 



l\CblfU)S(. 



THE IMtOPERTIES AND MOTIONS OF FLUIDS.* 



MI{. STANLEY has tukcu as tlio subject for tliis 

 work, Imving first made it the subject of pxpfri- 

 mcntal rcKcnrcli, t\w prnpcrtieji and motions of fluids, an 

 inquiry of cxtromo (liirn-ulty, and ho has troat<'d it with 

 groat skill and acumen. Anyone who ha.s stiuliid the 

 matlieniaticsof pneumatics, hydrostatics, and hydrodynamics, 

 and ho.s compared the jirocesses and results with those used 

 and obtained in the a])plication of mathematics to optics or 

 astronomy, knows how very far from exactness is all our 

 knowledge of the former subject";, and will recognise the 

 justice of Sir J. Ilei-schcl's remark, that "if there be one 

 part of dynamic science more aljstruse and unapproachable 

 than onother, it is the doctrine of the propagation of motion 

 in fluids." Even the doctrine of the tides, supposed by 

 many to have been thoroughly established since the time of 

 Newton, is as yet perplexed by the difficulties belonging to 

 all discussions of fluid motion.t 



It would lie an injustice to Mr. Stanley to attempt to 

 give anything like an abstract of its contents, for the 

 simple reason that though the book is no small one, it 

 presents a closely -reasoned account of the experiments 

 made by the author, and of the results to which they have 

 led. As the experiments actually made were in most cases 

 nearly ten times as numerous as those described, we may 

 regard the book as itself an abstract. 



The first three chapters are speculative, and in part 

 hypothetical ; they are generally attempts to apply 

 mechanical principles to hydrostatics, and " needed," JNIr. 

 Stanley says, " more leisure on some points than he could 

 command." Li the second chapter, tlie theory that liquids 

 hare tensile sui-faoos is opposed, the author's experiments 

 showing, in his opinion, that the surfaces of fluids are ex- 

 tensile, except in the case of free films, which are clearly 

 tensile in consequence of the position of the attractive 

 matter composing them. Some of the experiments illus- 

 trating this chapter can be very easily tried, and would be 

 of great interest to the student. For instance, here is an 

 experiment originally made by Descartes. An ordinary 



Fig. 1. 



sewing-needle placed on the surface of still water floats in 

 apparent contact with the water — see Fig. 1, presenting an 

 enlarged view of a section of the needle, and showing how 

 a bulk of water about eight times the volume of the needle 

 is displaced, so that the needle lies in a trough of the 

 deflected water. The conditions for making this experi- 

 ment most satisfactorily are described by Mr. Stanley, — in 

 particular, the surface of the needle should be perfectly 

 clean and free from the slightest speck of rust Then there 

 is a pretty modification of the experiment Take a 

 polished wire an inch long and about one twenty-fifth of 



• " Ex)icriiiienlaf licsoarckoa into tlio Properties and Motions of 

 flnidR, with Theoretical Deductions Therefrom." Br William Ford 

 Stanley. (E. i F. N. Spou, London.) 



t The oxplauatiun amusingly given in our books of geography 

 and oloinentary nxtronomy is uliout as vuluablo as the statement 

 that a top hold oslant will fall if lot go, rc^ardod as an explanation 

 of the fact that a 8j>inning top will not full though its axis be aslant. 

 It in simply an imperfect account of the statical theory, according 

 to which there would bo high water under the moon and opposite, 

 whorcoii, accortling to tho true theory, there would be high water 

 thoro but for frictional effects. 



an inch in diameter, well cleaned with potash liquor, and 

 wiped on a clean cloth. Carefully attacli to each end, upon 

 one side of the wire, a fibre of cotton silk, by means of 

 shellac varnish. Place tlio suspended wire in the centre of 

 a vessel, and pour in water till the wire is nearly reached. 

 If now we tak(! a small syphon of glass, filled with water, 

 and place one end deep into the vessel already described, 

 and the other end in another vessel containing water ; 

 then by raising or lowering the second vessel we may very 

 slowly raise or lower the water to or from the suspended 

 wire. If the water be raised, the wire will float as in the 

 former experiment If we lower the water, the wire as it 



Fig. 2. 



comes above the surface will draw the water with it 

 When the elevation is at a certain point, the same form of 

 curvature, but inverted, will be produced as was seen in 

 the depression. 



Another experiment, illustrated in Fig. 3, is important 

 The figure explains itself, only it will be understood that 

 there must be a can of water from which a small caoutchouc 

 tube supplies the jet : — 



Height of projection of free jet in air li inch, distance 

 5 inches. Immersing the jet for an instant, and then 

 restoring it to its place, so as to carry up a film of water : 

 height of projection with this film i an inch, distance 

 1| inch. 



The third chapter includes experiments illustrating 

 the passage of water through various apertures and 

 passages ; also a discussion of the passage of water past a 

 peg or post in a flowing stream, showing how the current 

 divides before reaching the place of absolute resistance 



^m 



(Fig. 4). This illustrates, Mr. Stanley believes, the di\-ision 

 of the great Atlantic equatorial current 300 miles before it 

 reaches Cape St. Roque. 



But we would direct the reader's special attention to 

 Chapter IV., in which the theory of rolling contact of part 

 of a fluid system is discussed, a theory bearing in a most 



