114 WHALES 



deliberations did not lead to an entiiely satisfactory conclusion, it has 

 nevertheless by now become clear what the crux of the problem is, and 

 where its solution must be sought. 



The speed of a body in water depends on its kinetic energy on the one 

 hand, and on the resistance of the medium on the other. The resistance 

 depends not only on the density and viscosity of the medium (in syrup, 

 for instance, it is greater than in water), on the body's velocity (to be pre- 

 cise, on the square of the velocity) and on the surface area presented to the 

 medium, all of which are known for Cetaceans in water, but also on the 

 nature of the flow past the body. When a fluid flows past a streamlined 

 body, as happens during the body's motion through the water, the 

 particles of the fluid in the immediate vicinity of the body are held on to 

 it and retarded in their original motion. The fluid layers lying farther 

 and farther away from the body are retarded less and less until we reach 

 the region of steady flow. If the drag on the particles nearest the body is 

 small, the outer layers execute a gliding motion over one another, and we 

 speak of laminar flow. However, if the drag becomes too great, the inner- 

 most particles are so slowed down that they no longer glide within the 

 outer layers. Their velocity is then called the critical velocity, at which 

 laminar flow changes into turbulent flow, and eddies are formed. Now 

 turbulent flow of the medium greatly impedes the motion of the body 

 placed within it. The nearer to the front of the body the source of the 

 turbulence, the greater the adverse effect. 



So much for resistance. We cannot solve the question of how much 

 power a whale must develop to overcome this resistance until we have 

 learned that the amount of work a single muscle fibre of given length and 

 thickness can do is by and large the same for all healthy animals. Thus 

 if we know the power of one animal, we can calculate the power of another 

 from its total muscle fibre, though other factors must also be taken into 

 consideration. Luckily, the effect of these factors can be determined from 

 a formula, and so, once we know the work a man can do - and man has, 

 after all, been studied more extensively than any other animal - it is 

 easy to determine what work a whale or dolphin can do, also. 



Now, scientists, and particularly Prof. Gray and A. V. Hill, have 

 calculated that a dolphin making 15 knots must develop 0-235 ^.p. to 

 overcome the resistance of the water. This is the same amount a man of 

 equal weight must develop in order to climb a mountain at the rate of 

 5 m.p.h. Most men would boggle at this task, though it is by no means 

 beyond the realms of human endeavour - a trained athlete can develop 

 as much as 0-35 h.p. Thus the dolphin is by no means an unusual animal 

 in that respect provided - and this is an extremely important stipulation - 

 we have been right in assuming that the flow along the entire body is 



