546 



HYDRODYNAMICS. 



Resistance No. 1, had the immersed part = a rectangle of 1 foot 

 ^ _', of base upon 1 foot of height. 



Resistance No. 2, had 2 feet of base upon 1 foot of height im- 

 f vessels mersed. 



-.n narrow No. 4, and 5, had 19 inches 8 lines upon 12 inches 

 5^ lines immersed, and differed only in their 

 lengths. 



No. 6, had its section like the great section of a vessel, 

 and the area of the part immersed was 190 

 square inches. 



The following Table shews the results of the experi- 

 ment : 



TABLE Shewing the Resistance of Boats in Narrow 

 Canals. 



From these experiments Du Buat has concluded, 

 that a canal cannot be considered as of indefinite width, 

 unless its width is 4.46, or 4| times that of the vessel; 

 or what is the same thing, that when this is the ratio 

 between the width of the vessel and the canal, the ves- 

 sel experiences the same resistance as if it moved in 

 the open sea. In order to confirm this result, the fol- 



lowing experiments were made, 



in which -r- and R in 

 b 



the last column are calculated by reducing the canal to 

 4| times that of the vessel. 



The law of oblique resistances does not appear to be Resistance 

 the same in a narrow canal as in a fluid of indefinite of f 

 extent, and an angular prow added to a prismatic ves- j,^^ 

 sel produces a less diminution of the resistance as the O f vesse ] s ;, 

 canal becomes more narrow. M. Du Buat expresses narrow ca- 

 the resistance of an angular prow in a narrow canal by nsls. 

 the following formula : 



r = R-R--l. in which 



5.46 



R is the resistance of a plane prow in a narrow canal. 



r the resistance of an angular prow of the same base. 



q the ratio between the resistances of these two prows 

 in an indefinite fluid ; and 



p 



the ratio of the section as formerly. 

 b 



When the boat No. 2. had an angular prow of 45, 

 and moved in a canal 28^ inches wide, and 15^ deep, 

 the resistance was 4.42 ; whereas, the formula gives 

 r = 4.444. 



When the same boat had an angular prow of 14 3', 

 the resistance was = 3.2 ; whereas, the formula gives 

 r = 3.25. 



When these experiments were repeated in a canal 

 shut at both ends, the resistance of boat No. 1. was 

 sensibly the same as when it was open; but when No. 2. 

 was used, the resistance was considerably augmented. 

 The effects in this case become very complicated, par- 

 ticularly for a canal which is short. When the sluices 

 in canals are three or four miles distant, the part of 

 the canal may be considered as of indefinite length, and 

 if approaching one of its extremities, the boats ought 

 to experience more resistance from this cause, yet the 

 heaping up and the driving back of the water obliges 

 the boats to rise, and thus allows the fluid to escape 

 more easily behind. 



3. Account of the Experiments of Vince on the Resist- 

 ance of Fluids. 



The experiments of Mr Vince on the resistance of Account ol 

 fluids, were published in 1798, in the Transactions of Vince's ex 

 the Royal Society of London. They were made with P etim 

 bodies moving at a considerable depth below the sur- 

 face of water, and the resistance was measured both 

 when the body moved in the fluid, and when the 

 body was struck by the fluid in motion. The results 

 of his experiments on the resistance of a plane surface 

 moving in a fluid, are given in the following Table 



TABLE shewing the Resistance of a Plane Surface mov- Resistance 

 ing in a Fluid tvith a Velocity of 0.66 of a Foot in a when the 

 Second, and inclined at different Angles 'to the Line off 

 its Motion. 



