6 
In the first place, in an actual ship there are two chief 
pressure systerns, one associated with the entrance at the 
bow and the other with the run at.the stern. The undula- 
tions caused by these are superposed upon each other, and 
the result is that the resistance curve is sometimes above 
and sometimes below a mean curve, according as the crests 
of one group coincide with the crests or with the troughs 
of the other group of waves. It appears probable that the 
variations from a mean value R can be represented by an 
additional term 61 cos (n/c?), where 6 and n do not involve 
e but depend upon the form and dimensions of the ship. 
In the second place, in addition to the transverse waves 
which we have considered alone so far, there are waves 
diverging from the. bow and stern. Regarding these as 
wave-trains inclined to the direction of motion, certain 
considerations suggest a similar form for the resistance as 
before, but with a value of c! one-third its value for the 
transverse waves. This term is found to have a small value 
compared with the others, and is only of importance 
relatively at lower speeds. 
Summing up the various terms we obtain a general 
formula of the type 
3 A) —3 (2) 
R=ae iC: +B (l-y cos iy )é NG? > ©) 
An inspection of experimental results shows that some 
of the coefficients in this formula may be given fixed values 
provisionally, that is, they are practically the same for 
ordinary types of vessels; thus we find c'=1°3, n=10°2, and 
y=014 approximately. A good agreement can be obtained 
at values of c greater than 1 by using only the second term 
in (3), but if we wish to cover the whole range by one 
formula we must include all the terms.* For present pur- 
poses we use (3) in the form 
_ 2°63 . 2:53 
R=ce % 48(1—0:14 cos ye CH) aay mylyn) 
* Loc. cit. ante, p. 215. 
64 
