PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 553 



well of Cambridge, ^fassachusetts, shows distinctl}^ how large guns may 

 be made of these stroDg materials, and triumphantly points out, by calcu- 

 lations which cannot be disproved, that the pressure of gunpowder can be 

 resisted by guns made upon his plan, even upon the supposition that the 

 pressure is enormous; and that there are no fissures or tendency to them, 

 but the reverse state of initial tension; but his imitators, in carrying out 

 his theory, have failed as others have done before; an evidence that the 

 guns fail from some cause not understood, and other than the direct pres- 

 sure of tlie powder. And liundreds of the heavy rifles of Admiral Dahl- 

 gren having been abandoned because of the liability to bursting; the large 

 number of Parrott guns that have failed in service, and during proof; the 

 spontaneous bursting of Rodman guns; the enlargement and fissures in 

 solid forged guns; the mysterious and uncertain endurance of all built-up 

 guns, by whoever made, either by bursting, distortion of the bands, or by 

 enlargement of the inner tube, and stretcliing the bands if ductile, and 

 breaking them if sti'ong and hard; points to the absolute necessity that 

 some new skill and class of ideas should bo engaged upon the subject. 



75. It is not a little gratification to American mechanics to believe that 

 the state of the art in foreign countries has not kept pace with our own, 

 notwithstanding the greater expenditure upon foreign ordnance, and that 

 we have so clear a field, which we may enter, and distance all competitions, 

 if we utilize the energy, genius, and skill of our artizans, not. heretofore 

 brought into requisition. 



THE DAHLGREN GUN. 



76. The Dahlgren gun is a shell gun, and is the most beautiful gun in 

 any service in- the world, but it is believed that more effective guns are 

 now required for attack on iron-clad ships. The first Monitor was armed 

 with guns of this class; and great reliance was placed on them in case' 

 that certain wrought iron solid projectiles, prepared for them, were to be 

 used in finy encounter with the Merrimac; but it is understood that the 

 inventor forbade the use of the latter, even with the fifteen pound charge 

 of p<»wder. Lest his directions should not be obeyed, it is said that lie 

 caused them to be taken off the Monitor, while she was at anchor in Hamp- 

 ton Roads, and certain other hwllow shots, covered with bronze, substituted. 

 ShsUs broke against the aides of the Merrimac, inflicting no injury. Uence 

 the Merrimac continued to be the terror to our army and navy for a long 

 critical time. But for this we might have captured Richmond sooner than 

 we did Yorktown; and who can conceive or estimate the cost of life or 

 money that has resulted? 



77. Other eleven-inch shells have been projected against iron sides without 

 effect. We must have better guns than these to meet the requirements of 

 modern naval warfare. 



TBE RODMAN GUN. 



78. Next we have the Rodman fifteen-inch gun, cast hollow, and cooled 

 from the interior, the object attained by which is to freeze the metal from 

 its liquid state immediately surrounding the bore first. As the heat is 

 nearly all withdrawn from the cast block through the surface of the bore, 

 successive strata of the iron freeze and contract upon the stratum within 



