THE LAWS OF FLUID EESISTANCE. 119 



that the forces there developed by the inertia against 

 the body must of necessity push it forwards exactly as 

 much as they push it backwards, and that when the body 

 is moving through a frictional fluid, or when it is moving 

 at the surface of a fluid, this balance is only more or less 

 destroyed through the operation of conditions which are 

 totally independent of the area of midship section or area 

 of ship's way. 



For this reason, the only instances I have time to give 

 you of the application of our knowledge of the causes of 

 resistance to practical questions shall be directly appli- 

 cable as illustrations of the fallacy of the midship section 

 theory. 





IG. 19. 



Let us suppose that Fig. 19 represents the respective 

 water-lines of two vessels of the same tonnage but of 

 different proportions of length to breadth. Now it is true 

 that the shorter of the two, when the speed of the wave 

 appropriate to its wave features is approached, will ex- 

 perience great wave-making resistance, and will therefore 

 probably experience greater total resistance than the longer 

 ship. But it is certain that at low speeds when the wave- 

 making resistance of both ships is practically nil, the 

 shorter ship will make the least resistance, because the 

 long and narrow one has the largest area of skin, and will 

 therefore have the greatest surface-friction resistance. 

 Judging, however, by the midship section theory, we should 

 have erroneously concluded that the short and broad ship 



