3^4 LECTURE XXX. 



^pths> that of the atmosphere ought by no means to be omitted in the cal- 

 culation. But if a more correct mathematician and mechanic would take the 

 pains to model Juan's book anew, to correct his errors, and to adapt his 

 modes of calculation to the laws of resistance previously deduced from ac- 

 curate experiments rather than from theory, there is no doubt but that the 

 work thus modified might essentially improve the science of seamanship. 

 He alleges indeed that the results of his calculations are in almost every in- 

 stance rigidly conformable to observation and experience, but it is probable 

 that where such a coincidence really exists, it must i)e owing to some com- 

 bination of errors compensating each other; and it is indeed very possible 

 that his calculations, with all their errors, may approach nearer to the truth 

 than the imperfect approximations which had been before employed. Juan 

 has generally made use of the English weights and measures, on account of 

 their convenience in computations respecting the descent of falling bodies 

 ^nd the impulse of water. 



The works of Chapman and of Romme, upon various departments of sea- 

 manship, possess also considerable merit. These authors appear to have 

 avoided the errors of Juan, but without entering so minutely into the detail 

 of nautical operations as he lias done. 



The accurate experiments of Dr. Hutton and of ('ount Rumford on the 

 force of fired gunpowder, and the resistance of the air, deserve to be men- 

 tioned as affording valuable materials to the speculative investigator, and 

 useful information to the practical gunner. Robins had very erroneously 

 supposed that the whole of the effects of gunpowder might be derived from the 

 expansive force of fluids permanently elastic; but Vandelli soon after main- 

 tained a contrary opinion in the commentaries of Bologna, and Count Rum- 

 ford has very satisfactorily shown the insufficiency of the agents considered 

 by Robins, although he has been unsuccessful in attempting ta deduce th» 

 ■whole force from the elasticity of aqueous vapour alone. 



The theory of practical hydraulics, as affected by friction, may be consir 

 dered as having been began and completed by the highly meritorious labours 

 of the Chevalier du Buat. He had some assistance in expressing the results 

 of hh experiments by meana of general rules or formulae^, aad. these, air 



