I The Sews,i The Hebe] movement 111 Pennsylvania , during the !:»«.{, (wonty-foiir hours have assumed *tn activity, as weft as a magnitude, which i.s lapidly solving Lite, mystery thai. surrounded Lien Lee's objects, and rendering every hour big with events. Whilst the main column of. his army moved upon ilai risbur and commerced the attack upon the works hastily erected for the defence of the city, another column moved to Gettysburg, and front thence sent out a heavy detachment of cavalry, who struck the Northern Contra! Railroad at Hanover Junction, and, moving Northward, destroyed two bridges on the lino of the railroad between that point and York. The latter place was occupied by the Rebels on Saturday afternoon, and two bridges beyond, toward Harrisburg, were also destroyed.— The same body ol cavalry, it is supposed, also advanced to Wrightsville, on the right bank of'the Susquehanna, thirteen miles, Prom York. Our forces then fell buck to, Columbia, on the other side of the river, I and it is feared that the bridge, a fine ! structure a mile and a quarter long, wilt bo j destroyed. There were reports that the I Rebels had aLo struck the Pennsylvania1 Railroad at Duncamiou, nine mites above Harrisburg, but latter despatches contradict this vepoit