BoetoD, Juno 22. A letter from tho blookading Heet off Charleston says that on the bvening of tho 12ih inst. the robel batteries on Morris Isiand opened Ero on tbe troopfl on Folly Island, and for hali an hour no notice was takonof' tbe firing by our forco3. Presently tho gunboats Pawneo and MoDonough stcamed up to within ffood rango oí tho robel batteries and poured in a tleadly fire from their heavy guns. The Union batteries on JFolly Island now oponed their fire, and for three hours the shot and sliell ffew thick and fast. Wo coulcl seo that the rebel shot feil short, while those from our batteries and gunboats burst in tho midst of the rebel batteries. Tho firing astod until sunsst, but tbe rosult was not iully known. The robels wero seon carrying oö a nuniber of killed and wonnded. During the firing the rebel rams camo out from behind Sumter,and pro. coeded down about two miles ('rom that fort vvhero they remained until tho engagement was over, not daiing to fake partin tho fight. The samo night the whole roadstoad and 'ebipping were brilliantly illnininated for soveral hours by an extensivo confiagration in Charleston. The hoavuns were lighted up for miles around.