^ Capt. M^KonocWie on the most effectiW use of' 



or two points of which would be directly beneficial. It is this; 

 last consideration, I apprehend, which chiefly accounts for the 

 general superiority of an external drag over an internal rota- 

 tory impulse ; and the dispersion of power thus contemplated 

 must evidently be proportionate to the weight of the vessel in 

 which a steam-engine is embarked, and to the consequent mo- 

 mentum with which she scends aft in a head-sea. It must be 

 greater consequently in a large boat than in a tug. But the 

 others are interesting also, as particularly applying to the case 

 under review ; and it is satisfactory to find the conclusion to 

 which they lead, supported by analogous results in cases too 

 different, it is true, to be considered positively corroborative, 

 but from which a general principle may notwithstanding be in- 

 ferred. A horse will draw considerably more than three times 

 as much as he will carry ; and locomotive engines of six or 

 eight horse power, and weighing, carriage and all, not above 

 fifteen tons, will draw ninety tons, at the rate of nine miles an 

 hour after them, when it is very certain that thirty tons piled 

 above them, with the friction of one-fourth of the superincum- 

 bent weight (which is that of iron upon iron) would go far to 

 anchor them at once. These engines, indeed, are usually cal- 

 culated to have seven-eighths of their power disposable for the 

 purposes of draught ; and with this, as above, to draw six times 

 their own weight on a dead level, with considerable speed. While 

 steam-boats, as usually constructed and employed, cannot em- 

 bark above the odd eighth part of their own weight and bulk ; 

 and, in circumstances of very ordinary difficulty, are almost uni- 

 versally complained of as deficient of power, even for their own 

 impulsion. 



Waiving, however, these presumptions for the present, thus 

 far may be considered certain. A smaller power will move a 

 greater weight on the tug than on the carrying system ; the dif- 

 ference is, by a fair induction from actual experiment, not less 

 than as three to one ; and there is much in the entire circum- 

 stances of the case to make it probable that it is even a great 

 deal more. 



7. Wherever there is shoal water to contend with, the tug 

 system seems peculiarly applicable. A large steam-boat, with a 

 powerful engine, necessarily swims deep ; and, accordingly, the 



