Boston, Juuc 8, 1861. The following is an extract of a letter froia an old and distiuguished officer of the U. S. Aruiy to a fricad in tbis city : Chaiubcrsburg, June 5. We are here uow witl) 15 regimeuts, not yet i'ully equipped, but all enger lor a coullict. Uur destiiiatiou is Hurper's Ferry, and in a few days we sliall advauce to the coigtiborliood, when eithur a retruit or a shaip conflict awaits the rebels - Gen Scott's plan, whicli all good uien admire, -is to uiovo slowly but Buraly forward, to uitimate viotory, without leaviug niuch to chance, and to sjwre tht uuiiccessary efiusions of blood; He is playing this great gamo of war as ho would play a game ot' ciiuss, and if his lito is spared and ihe edituis and politiciuBS will let him alone, he will fioisfa it iu about one year. It', howuver, hu is uiterfered with by tho popular voiee alludod to, it is inipussible to say wheu the war will end. - Uouiidunt in iis superior strength, thu iSorlh eau aÜonl to Hwait thu judioious arraugeiuüuts of our jreat war fcfaief, anu l hopu, it will coueluiiu to qo so. Uur öuwcss dependo upou it.