SIR ROBERT WALPOLE.Whilst Washington man?uvred to prevent Howe from crossing the Schuylkill above him, the English General crossed below on the 22nd of September, and thus placed himself between Philadelphia and the American army. It was now necessary for Washington to fight, or give up that city; but the condition of his troops, deficient in clothes and shoes, owing to the poverty of the commissariat department, with wretched arms, and fatigued by their recent exertions, forbade all hope of maintaining even the defensive. He therefore fell back, and Cornwallis, on the 27th, advancing from Germantown, entered Philadelphia amid the welcome of the loyal inhabitants. Cornwallis occupied the city with four regiments, but the body of the British army encamped at Germantown, ten miles distant. But, though the Americans had evacuated the city, they still held the command of the Delaware below it, and thus cut off the supplies of the British army by sea, and all communication between the army and the fleet, except by the circuitous course of Chester, liable to capture by the enemy.