MECHANICS AND USEFUL ARTS. 57 



own guns of avail; and, when opposed to any but these heaviest 

 pieces, will still be in effect impregnable. The case of the Monitor 

 and Merrimac affords an illustration. No one supposes that either 

 of these vessels could have escaped serious injury if subjected to a 

 course of target firing from the most recent and powerful descriptions 

 of ordnance ; yet they sustained for four hours the utmost effort of 

 each other's batteries. The Monitor was hardly more than scarred 

 by the fire of the very guns which, on the preceding day, had, in a 

 fourth of the time, acted most destructively on the hulls and crews 

 of two fine wooden frigates." 



With regard to the opinion which prevails in England, that solid 

 plating is superior for resistance to several plates combined, Capt. 

 Dahlgren says: "Practice in the United States proves that several 

 plates made into one are preferable, on many accounts, to one solid 

 plate, and would be so altogether if it were not for the increased 

 number of bolts that become requisite, and are the weakness of all 

 such plating. Indeed, even with this disadvantage, it remains to be 

 seen whether, by any process, a very thick solid plate can be made 

 equal in its texture to the thinner plates. For in every instance 

 where I have seen a solid plate pierced by a shot, the imperfection at 

 the welds has been made manifest by their separation, although exter- 

 nally none such could be perceived." 



Capt. Dahlgren also states that the results of his experiments favor 

 the use of " cast" rather than of " wrought " iron shot. " The cast- 

 iron shot does break, and the wrought-iron is only crushed ; but while 

 the latter lodges in the four-and-one-half inch plate, the former 

 (both being of eleven inches) passes completely through the plate, 

 and nearly through the wooden backing of twenty inches, making a 

 larger hole, and badly cracking the plate." 



" The operations that have been conducted in the United States," 

 continues the writer, " with reference to the power of different can- 

 non and projectiles, as well as the resistance of iron plating, have 

 been so far satisfactory that the results derived have been consistent. 

 Still they are liable to such qualification as may be properly due to 

 practice upon targets only, and in some sense favor the defence, 

 because many sources of weakness which are unavoidable in the 

 extensive structure of a ship are undisclosed in the strong, new, and 

 well-knit target, but will appear when vessels are subjected to fire 

 and to the wear and tear of time and service, especially at sea. So 

 long as the ponderous armor is merely attached to the ship, and is not 

 made to contribute to the strength of the fabric, but severely taxes 

 that strength, so long will there be involved a serious element of 

 deterioration, which will after a while impair the general capacity 

 for endurance, and in the end unfit the ship for battle. In this 

 respect, as in many others, the turret class are to be excepted from 

 much of the preceding remark, and are probably of greater and 

 more certain endurance under severe fire than the ordinary plated 

 vessel. So far, they are likely to find the most fitting sphere for 

 their peculiar powers in the less troubled waters of harbors and riv- 

 ers ; though the ability that has devised them may also be able to 

 give a wider scope to their usefulness." 



Armament of Iron-Clad Vessels. Capt. Dahlgren also states hi* 



