ANTMAL MECHANICS. 



47 



surements by means of which the following calculation is 

 made, were kindly furnished to me by Dr. E. A. Parkes, and 

 by Mr. Maclaren, of Oxford. 



The Kesistance offered by the water to the motion of the 

 boat is divisible into the following parts, due respectively to, 



1 . The Distortion of the particles of water ; 



2. The production of Currents ; 



3. The production of Waves ; 



4. The production of Frictional Eddies. 



In the case under consideration, the first three causes of 

 Resistance may be neglected, in consequence of the " fair" 

 form of the boat, and of the limited speed at which she is 

 driven ; and the whole resistance may be regarded as due to 

 the production of Frictional Eddies. 



In discussing the amount of Resistance due to this cause, 

 I shall adopt the principles laid down by Professor Rankine,* 

 from which it appears that 



The Eddy Resistance = 



where ds denotes the element of the boat's skin ; 



q, the ratio which the velocity of gliding of the water 

 over that element bears to the speed of the boat ; 

 c, the speed of the boat ; 

 g, gravity; 



w, the specific gravity of the water, or weight of one 



cubic foot ; 

 /, the coefficient of friction (=0.0036). 



In this equation, \qHs is the augmented surface of the boat's 

 skin, and is supposed to sum up together the skin resistance 

 and that due to the excess of water in front, and to the defi- 

 ciency of water behind. 



* "Treatise on Shipbuilding," Fol., Mackenzie, London, 1866, pp. 78 etseq. 



