NORTH-WEST PASSAGE. 25 



ten ruined. The fact is, that the materials of 

 which the largest vessels are huilt, are only of the 

 same strength as those used in the construction 

 of the smallest, while the timbers and planks 

 in a line-of-battle ship, when compared with those 

 of a small vessel, are by no means of a thickness 

 proportionate to its tonnage. Hence a large vessel, 

 however firmly built, can never possess the same 

 comparative strength as a small one. Besides, the 

 momentum of a large heavy vessel striking a rock, 

 a mass of ice, or other similar body with a given ve- 

 locity, is so much greater than that of a small ship, 

 that the difference of the shock is vastly greater 

 than the difference of the strength of the two. 

 Thus, we will suppose, the weight of two vessels 

 with their ballast and stores, one of 400 tons and 

 another of 100 tons burden, to be proportionate to 

 their tonnage, and that they both strike an immove- 

 able mass of ice with the same velocity, say, six 

 miles per hour. Then the momentum of the for- 

 mer will be represented by the number 24, and 

 of the latter by 6, or as four to one, being in the 

 same relation as their tonnage. But the comparative 

 difference of strength of the two, we know, will pro- 

 bably be not greater than as two to one; consequent- 

 ly, the capability of the smaller vessel for resisting 

 the concussion, will be twice as great as that of the 

 larger ; or, in other words, the vessel of 100 tons 

 burden, would bear a blow impinged with a velo- 

 city of eight miles per hour, as well as the larger 



