VOL. LXXXVI.] PHILOSOPHICAL TRANSACTIONS. GQS 



made to ascertain the advantages which result from adhering to the constructions 

 prescribed by practice, compared with those which are consequences of following 

 the deductions from theory; and lastly, if any new forms of vessels, disposition 

 of parts, or otiier varieties of construction, have been discovered by considering 

 this subject in a theoretical view, and in what degree these inventions have been 

 found advantageous when applied in practice. 



Exclusive of the application of geometrical principles,* by which the forms of 

 vessels and the disposition of their most esssential parts are ascertained, theory 

 may be considered as bearing to naval architecture a two-fold relation : first, as 

 depending on the pure laws of mechanics, a subject on which the preceding 

 cursory observations have been offered : 2dly, the practice of naval architecture 

 is guided, in most parts of the world, by a species of theory or systematic rule 

 which individuals form to themselves from experience and observation alone : it 

 is founded on the experimental knowledge in naval constructions, which has 

 been transmitted from preceding times, combined with the more recent improve- 

 ments, and includes whatever inventions of skill and ingenuity are applicable to 

 the various machinery that is employed in the construction and management of 

 vessels ; by repeated observation on the forms, proportions, and equipment of 

 ships, and by attention to their excellencies and defects when afloat at sea, faults 

 are remedied, good qualities are improved, and rules of practice are by degrees 

 established according to principles, well perceived and understood, without much 

 assistance from the theories of mechanics, statics, and geometry, on which such 

 principles are founded : for in this, as well as other instances, it is well known 

 that skilful practice, aided by long experience, arrives at determinations which it 

 is very difficult, sometimes impossible, for theory to infer : on the other hand it 

 must be allowed, that pure theory, depending ©n the laws of motion, the sub- 

 ject of disquisition in the works of Euler and Bouguer, is of great importance 

 to the advancement of this science : for by such investigation, so far as the data 

 are sufficient, the qualities of vessels are traced to their true causes, and are 

 explained by general laws : whereas the principles derived from mere observation 

 are scarcely ever applicable beyond the cases in which they have been experienced 

 in practice. 



• Practical treatises on ship-building have been published by various authors, particularly by M. 

 Clairbois, Romme, and Fred. Chapman. In these useful works, theory is occasionally applied to 

 explain and illustrate the principles of naval architecture ; but no accounts are to be found in any 

 of these volumes, as far as my researches extend, by which the constniction of vessels, founded on 

 theoretic investigation, have been subjected to practical examination during voyages. M. Chapman, 

 in page 79 of his work (Paris edit.), expresses the proportions and disposition of parts in vessels by 

 algebraic quantities, which however are not to be mistaken for deductions from tlieory ; since the 

 author has not pointed out any mode of investigation, or train of reasoning, by which those expres- 

 sions can be deduced from the principles of mechanics. — Orig. 



