
. 

TRANSACTIONS OF THE SECTIONS. 31 
: and yet to swim very light. Besides, this vessel was to be able to go backwards as 
well as forwards equally well, and though a small boat was to contain great accom- 
modation. 
Now it will be easily seen by those accustomed to the wave system, that the pro- 
blem as thus stated is one to which the wave principle -is far from seeming pecu- 
liarly applicable. In the first place, it is well known that the wave principle pre- 
scribes a different form of the bow for that of the stern, in order to obtain most 
speed with least cost of power. In the second place, it is known that a high speed 
requires, on the wave system, a very considerably greater length than was here al- 
lowed for the entrance of the vessel, or the lines of the bow. It would therefore 
seem at first to be a case that would in all probability prove too difficult for the 
successful application of the wave system. It is on this account mainly that this 
case seems to me important to the science of naval construction, and to the progress 
of the wave system, and to the records of the British Association. 
There is one more feature in the case which gives it interest. At the same time, 
the same problem was worked out by another party on another plan of constructioa, 
not on the wave principle. Another vessel was built under similar conditions, and 
furnished with engines of the best construction, made by one of the most eminent 
engineers in England. Both these vessels were built at the same time, and tried 
under similar circumstances ; therefore here was a case in which the practical value 
of the wave principle has been brought to a test more direct and less questionable 
than any that was likely to have occurred, and therefore more important to be placed 
on the records of the British Association. 
The first question which will naturally occur to a Member of this Association 
who recollects this principle, will be this: how could you apply the wave principle 
in a vessel made to go equally well both ways? The first answer is ready—it is 
this, that the vessel cannot be made to go as fast as if designed with equal power to 
go only one way, seeing that in one case she would have a best possible bow and a 
best possible stern, and in the other case could have neither. 
The next point is this, that in both cases, of bow and of stern, it was necessary 
to have acompromise. Each required to be in turn both bow and stern; this was 
accomplished in the following manner :— 
If there be any point which has more forcibly struck me in the application of the 
wave principle than another, it is the flexibility of the wave principle—the extent 
to which it admits of deviations from its strict rules without losing the benefit of its 
resistance. If it had unluckily been true of this system, that it prescribed an exact 
mathematical solid in its three dimensions (like Newton’s solid of least resistance), 
to which implicit adherence was imperative, on pain of losing all the benefit prof- 
fered, then indeed the system would have been (like Newton’s) of little use, from 
the fact that from causes independent of resistance, ships cannot be solids of revo- 
lution, consistent with other qualities. The wave principle, on the contrary, pos- 
sesses wonderful flexibility, first from the circumstance of its prescribing lines in one 
plane only, and so leaving the other two dimensions in the hands of the practical 
constructor, so that the sections of the vessel in one plane being given by the system, 
_ the sections in two others are at the service of the constructor. This to the accom- 
plished constructor is the greatest possible benefit; to the ignorant constructor it 
may be considered a great disadvantage, because it affords him no fixed rule in two 
planes, and so leaves him open to commit a multitude of other errors in points which 
are not questions of resistance; but to the scientific constructor it gives precisely 
that latitude which he desires, to leave him free to work out the intentions of the 
owners and the uses of the ships he may have to build. 
_ There is a second point in the wave system, which is another element of its ge- 
neral usefulness—it partakes of the nature of a mathematical maximum or minimum. 
It is the peculiarity of a ‘“‘ maximum and of a minimum,”’ that deviations on either 
_ Side of it to a moderate extent occasion deviations of magnitude that are compara- 
tively very small. Thus it is that the wave line being considered as the curve of 
Teast resistance, there are near to it an infinite number of approximate curves, which 
‘are curves of small resistance, though not of least; and out of these the constructor 
_ is free to choose those which shall best accomplish any other object, at the sacrifice 
of the smallest amount of resistance. 
