130 Mr. Atwood's Propositions determining the Positions , &c. 
with the alteration of the centre of gravity of the vessel, and 
the section of the water, to increase or diminish the stability of 
the ship ; and it must be added, that the inclination of the 
masts and sails to the horizon, and the direction in which the 
wind impinges on them, will suffer alteration from the same 
cause. 
Although theory alone may not be adequate to the solution 
of these difficulties, yet, when combined with experiments and 
obervations, it may be probably employed with great advantage 
in these researches. If the proportions and dimensions adopted 
in the construction of individual vessels are obtained by exact 
geometrical mensurations, and calculations founded on them, 
and observations are made on the performance of these ves- 
sels at sea ; experiments of this kind, sufficiently diversified 
and extended, seem to be the proper grounds on which theory 
may be effectually applied in developing and reducing to sys- 
tem those intricate, subtile, and hitherto unperceived causes, 
which contribute to impart the greatest degree of excellence 
to vessels of every species and description. Since naval archi- 
tecture is reckoned amongst the practical branches of science, 
every voyage may be considered as an experiment, or rather as 
a series of experiments, from which useful truths are to be 
inferred towards perfecting the art of constructing vessels : 
but inferences of this kind, consistently with the preceding 
remark, cannot well be obtained, except by acquiring a per- 
fect knowledge of all the proportions and dimensions of each 
part of the ship ; and secondly, by making and recording suf- 
ficiently numerous observations on the qualities of the vessel, 
in all the varieties of situation to which a ship is usually liable 
in the practice of navigation. 
