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LECTURES TO SCIENCE TEACHERS. 



would make the greatest resistance of the two at all 

 speeds. 



Next let us take the two ships, whose water-lines are 

 shown in Fig. 20. It may be seen that the one shown in 

 dotted lines has the same length, and the same sharpness 

 of ends as the other, but is filled out amidships to a larger 

 cross section. On the midship section theory, this one 

 would clearly have the greatest resistance of the two. Never- 

 theless, in the trial of two models of those lines it appeared 

 that at the higher speeds the form with the largest cross 



FIG. 20. 



section made considerably the least resistance. The expla- 

 nation of this lies of course in the fact that the addition 

 amidships, though increasing the displacement, forms a 

 prolongation of the wave features of the two ends, and thus 

 lessens the wave-making resistance. 



In conclusion, let me again insist, and with the greatest 

 urgency, on the hopeless futility of any attempt to theorise 

 on goodness of form in ships, except under the strong and 

 entirely new light which the doctrine of stream-lines 

 throws on it. 



It is, I repeat, a simple fact that the whole framework 



