48 



ANIMAL MECHANICS. 



From the value of the coefficient of friction employed 

 (which is deduced from Professor Weisbach's experiments on 

 the flow of water in iron pipes), it follows from the preceding 

 equation that at ten knots the Eddy Resistance is nearly equal 

 to one pound avoirdupois per square foot of Augmented Surface ■;* 

 and varies, for other speeds, as the square of the speed. 



The whole difficulty of the calculation of the eddy re 

 sistance turns upon the calculation of the augmented surface, 

 which is effected by Professor Rankine, on the assumption 

 (conformable to repeated experiments), that the augmented 

 surface and its resistance are the same as those of a Trochoidal 

 ribbon, whose length is the length of the boat on the plane of 

 floatation, whose breadth is the mean immersed girth of the 

 boat, and whose coefficient of augmentation is 



i + 4 sin 2 o> + sin 4 a>, 

 where &> is the angle of the greatest obliquity to the horizon 

 formed by a tangent to the Trochoid. 



Applying the foregoing principles to the sections of the 

 Oxford eight-oar when loaded with its crew,f I have found the 

 following results : — 



1. Length of plane of floatation = 52 ft. 



2. Girth of central immersed section = 31.5 in. 



(Mean immersed girth) = frds = 21 in. = 175 ft. 



3. Sine of obliquity = J. 



Hence the coefficient of augmentation is 



i+4Q) 2 + (i) 4 =i-254; 



and the 



Augmented surface = 52 x 1.75 x 1.254 = 114. 11 sq. ft. 

 The speed of the boat is assumed to be one knot in seven 



* It is exactly f £|ths of a pound. 



f The weight of the boat is 350 lbs., and the average weight of the crew is 

 u st. 4 lbs. each, and the coxwain is 8 stone. 



