591 Wave Resistance. 
in the general form of the curve. The effect of differences of form, other than 
the ratio of draught to length, is, of course, important, and the three curves 
reproduced in fig. 2 have been chosen so that this should not be overlooked 
in the comparison between the various curves. 
We note first the differences between the two sets of curves in fig. 2. The 
theoretical curves have much more prominent humps and hollows, due to inter- 
ference between bow and stern waves, especially at the lower velocities. This 
may be inherent in the approximations made in replacing the ship by a certain 
doublet distribution over the median plane. But the effect is probably due 
in part to the simplified form with constant horizontal section ; however, this 
point must be left for future examination. It is hardly necessary to remark 
that, when one reaches the stage of comparing absolute values, the influence of 
viscosity and turbulence must eventually be taken into account. Further, 
this consideration applies not only to the theoretical curves but also to those 
we have called experimental ; for the latter are derived from actual measure- 
ments of total resistance by deducting the frictional resistance calculated 
according to an empirical formula, the residuary resistance so obtained being 
chiefly due to wave-making. It may be that the effect of fluid friction on 
the wave-making could be expressed by a slight alteration of the equivalent 
wave-making form of the ship. The curves of fig. 2 show also small 
differences in the positions of the interference maxima, but this is, of course, 
due to the different lines of the various models. 
When every allowance has been made for differences of form and other 
considerations, the curves of fig. 2 show over a large range ol velocity a general 
agreement between theory and observation, which is very interesting and 
suggestive. Further approach to ship-like form may enable us to remove 
some of the remaining differences, and should in any case be of service 
in the interpretation of experimental results. 
HagRIson AND Sons, Ltd., Printers in Ordinary to His Majesty, St. Martin’s Lane. 
239 
