the Stability of Ships. 205 
ginates from experience alone, or from investigations founded 
on the laws of motion, is to be regarded as forming a part of 
this theory, in which, a constant reference to practice is so 
essentially necessary. For, although many principles are de- 
ducible from the laws of mechanics, which it is probable that 
no species of experiment, or series of observation, however 
long continued, would discover, yet there are others, no less 
important, which have been practically determined with suf- 
ficient exactness, the investigation of which it is scarcely pos- 
sible to infer from the laws of motion ; the complicated and 
ill defined nature of the conditions, in particular instances, 
rendering analytical operations founded on them liable to un- 
certainty. Since the practice of naval architecture depends so 
materially on the knowledge of the causes which influence 
the motion of vessels at sea, much benefit may probably be 
derived from the extension of well founded principles, both by 
attentive observation of the qualities of vessels, compared with 
their construction, as well as by investigation of the effects 
arising from particular modes of construction, depending on 
the laws of statics and mechanics, whenever the conditions 
admit of inferring principles which are clear and satisfactory, 
and easily applicable in practice. With a view to these ob- 
jects, so far as regards the theory of stability, the ensuing 
Disquisition has been written. 
When a ship, or other floating body, is deflected from its 
quiescent position, the force of the fluid’s pressure operates to 
restore the floating body to the situation from which it has been 
inclined. This force is distinctly described, in a treatise written 
by the most celebrated geometrician of ancient times, who 
uses the following argument for demonstrating the position in 
which a parabolic conoid will float permanently in given cir- 
