NO. 15.] 



EMPIRICAL LAWS OF RESISTANCE. 



131 



becomes 4 - 4 m. According to Froude's rule the maximum dead-water resi- 

 stance will then increase in the same ratio as the vessel's displacement. If 

 further, by a moderate alteration of its breadth, or its breadth and length, 

 the displacement be made equal to 800 tons, we may assume that the dead- 

 water resistance will continually alter, approximately as the vessel's displace- 

 ment, as long as its shape or "type", its draught and speed, and the water- 

 layers are unaltered. The whole reduction is, in consequence, made by increas- 

 ing the maximum dead-water resistance in the same ratio as the weight of 

 the boat, and the depth of the fresh-water layer in the same ratio as its mean 

 draught. The table below gives the numbers of the preceding table, reduced 

 in this way. 



The results contained in this table, are represented by the heavy curves 

 (1), (3) and (4) in Fig. 3 PI. XI, which give the maximum dead-water resi- 

 stance i as functions of the depth of the fresh-water layer. The faint curve (2) 

 shows approximately the velocity at which, according to the experiments, the 

 dead-water resistance would be a maximum (when the total depth of the water 

 is 37 m.); the velocities are plotted vertically in m. per second and the depths 

 of the fresh-water layer horizontally, on the same scale as in the case of the 

 other curves. [If the depth of the salt-water were infinite, and if the waves 

 created were very low, Curve (2) should theoretically have been a parabola]. 



1 In the figure stands "wave-resistance", which is not quite correct. 



