Fluid Mechanics of Swimming Propulsion 



principle has, however, so far remained a good challenge. The previous at- 

 tempts brought forth by Dr. Schwanecke will shed light to stimulate further 

 developments. 



I am particularly grateful to Professor van Manen for his contribution of 

 some yet unpublished results. His experiments with Dutch swimmers are most 

 intriguing, in that a method of separating the thrust from the resistance is pro- 

 posed. I certainly agree with him that these results should be viewed with cau- 

 tion since swimming is one of those physical motions in which the quantities of 

 interest, such as the thrust or the viscous resistance, when considered sepa- 

 rately, can hardly be observed without disturbing the phenomenon under obser- 

 vation. This is a kind of "uncertainty principle" that makes the problem inter- 

 esting and the solution difficult. The quantitative results of Professor van 

 Manen are nevertheless extremely enlightening. 



1205 



