The Advance On Charleston

liü ton Heao), Alarch 81. The flag-ship of Admrral Pupont, the Wabash, in tlie action :it Hilton Head, eigtitcen muiiths ago, at cvcry bro.vdside from twenty four guns, tlircw 1,000 pounds of solid shot into t lio rebol fcrtifications HergUDS, manv of tlicm, are 1 1-inch, the same caliber as most of thera iu tlie iron ciad flect, yet this vessel would be powerlcss against a Monitor. The tonnage oí tlie Wabash ís -1,274, hile that "of the Monitor is but 884. - 'J'he iron-clads of Iha Monitor class are concíTitrated powers. The fleet is composed of the fullowing vessels : q Timmer. G una. New Ironsides, Capt. T. Turner 3,480 18 Moniauk, Capt. J. S. Worden 881 2 Pasaaic, Capt Pereival Drayton .... fc84 2 Weskawken, Capt. Jolm Rodgers.. 864 2 Naliant, Capt. John 15ownes 884 2 Katkill, tapt. G. W. Kodgers 884 2 Patapscó', Oájpt. Daniel Animen 884 2 Nnnuicket. Capí. D. M. N. Fairfax, 884 2 Keukuk, Capt. A. O. lUiiml 740 2 Total 10,412 34 The irmament of tho New-Ironsides is sixteen 11-iiich guns, and two 200pound rifled Parrott guns. All of tho Monitor class exeept the Kcokuk have each a 11-inch and a 15 inch The Kookuk has two turrets, and a 11inch gun in each turret. The 11-inch guns tlirow a solid shot vveighing 180 pounds; the 15 inch guns thniw a solid shot weigbing 47G pounds. The total weight of metal which can bo thrwn at a single discharge sums up : Ponn:ls. 23 clcvcn-incli guns 4,500 7 lifteeri-incli juns 8,382 2 rwo liundred jxuuul 400 31 gims. 8,232 Bu! as the New Ironsides will be able (o use but ono broadside at a time in an attack upon Sumpter, one balf of her broadside guns should be deducted - 1,440 Ibs - which would give a total weight of 6,792 Ibs. of metal, which can be hurled at a given moment upon the rebel works ! Guns of so largo calibre cannot be fired rapidly. not oftener than six or eight times an hour. Time must be givec them to cool. Sixty times a day is probably the maximum. At that rate the expenditure of ammunition vvill be enormous. A single 11 inch gun iired sixty times, or once every ten minutes for ten hours, will tlirow ten thousand eight hundred pounds of metal. A 15inch gun fired al the same rapidity wil' require twenty eigh' thousand fice hundred and sxty pounds! Any ono of the Moiitor class will require thirty-nine thousand three hundred and sixty pounds - nenrly twenty tons nf shot ! Each Moni tor will also uso about two tons of powder per day. The entire fleet, working at the same rato, will hurí at the rebel fortifications four hundred and fifty thousand pounds of iron in ten hours, at an expense of fifty thousand pounds of powder ! or two hundred and twenty uve tons of shot and tweaty-five tous of powder. Many people have wondered at the long delay on the part of Admiral Dupont, but tbey will appreeïate tho magnitude of the tradeftaking when they learn that the ron-elad fleet would use up in six days twelve hundred tons of' -shot and sliell, and a hundred tons of 'powder! This is a maximum. The fire of the fleet uaniiot be thus sustained. It probably will fall fr short of it. But t'.iere are elements which have been taken irito tho calculation. But will this tremendous weight of metal be hurled with sufficient power to destroy the fortifications of the enemy ? It is an estiiHished rule that the penetration of prjecdles is proportionate direell- to their weight aml diameter to the square of their velocity. The theory of our artillerists is that a heavy shot throsvn as t necessarily must be at a comparatively low velaeity, of about 800 feet per second of initial velocity, is more destructive in the end than lighter projectiles thrown ut high velocitics. English artillerists take a different view, and believe that a lighíer shot thrown with almost lightning velocity will be moro effeotive. This point is not yet settlcd. The approaahing engagement will, perhaps, in a measure deiermine it. Admiral Dupont has large guns, and his fire must be slow, delibérate, and sustained. The rebels have some English Whitworth guns, probably geven or eight-iach caliber, throwing 125 and 150 pound shot. They will u.se high charges of powder - ■ twenty-five pounds - and obtaip, an initial velocity of 1500 feet per second: but even those chargos wtU nofc probahly pierce tho turrets of the Monitors. When wc spcak of a ball rnoviug it an initial velooity of 1.G00 feet per second, it is not meant that the ball actually passes through 1,000 feet in tho second, but at a given instant moves with a rate, which if continued, would produce that result. The moment a ball leavos the muzzle of a camión it begits to meet atmospherii; resistance, and il s momentuiTi is retarded 'i'he sitial -belocity of a ball is the rate per second at whieh it moves at the beginning of its flight. Atmos j)l]i,ic resistance is less iu the conical, elongatéd projectile than in the sphere. The Armstrong gun anJ the Whitworth gun throw elongatéd projectiles. It is not knovrn that the rebels have any of the Armstrong guns in position ; probably they have noue, as they are very costly, and also iuasnmch as tho English governmeut take all that are matiufactured. The iron-clads have pretty we.), tpsted 'horiginal Monitor in t&e ::ngagenient with tho Merriiiiuc, ihe Moniauk, l'assalo, apd Naha,ui 'ijt' Fort McAllister. - Torpedoes are more to be (eared than tho guns in the rebtl, fürts and batteries. Thero will bo poiuts whcre shots from 'Sumptev, Moultric, Fort Johnson, Morris Island, and Sullivan Island, will fall like bail around and upon the attaoking flcet, but tho swiftost flying bolts, the hcaviost shot, judgiug from what has been, will roll off harnilessly, leaving no dceper dents than the hailstoue of a June shower upon a shingled house-roof. Uut thero ia still an important point for consideration. Will tho thirty four guns be able to silonce the guns of the enemy 1 The effect of' the shot thrown against Fort Pulaski at a distanee of three-fourths of a mile ia good data. The first day's tiro cracked and erumbled the masonrj'. When the white flag uas rais cd the wüII was a ruin. If this was accompüsbed at such a distanee, it is reasonable to conelude that the 15-iuchguns at onethird the distanee will be ablc to breach the walls of Sumpter. Against earthworks no exporiment, bas been made except at Fort McAllister. There the fire was delibérate. The twenty five feet embankments were badly torn. One gun was dismounted, and this at the distancu of a mile. Eurthworks are stronger dofenso tban maaonry. Tbey can be repaired at night and mude al most ns good as new. But the fleet will not be coinpeüed to silence them bcfore reaehing Charleston. Thcy can be passed by W'ith impunity, at least such is the supposition. J3 u t when there is so much that is new and untried - new gnns, great guns, new inaehinery, now defensive and offensiye appliances, no satisfactory conclusión ean be arrived at. We must wait for the trial.