Sir William Howe passed the night of the 11th on the field of battle. On the succeeding day he detached Major-General Grant with two brigades to Concord Meeting House, and on the 13th (September, 1777), Lord Cornwallis joined General Grant, and marched toward Chester. Another detachment took possession of Wilmington, to which place the sick and wounded were conveyed. To prevent a sudden movement to Philadelphia by the lower road the bridge over the Schuylkill was loosened from its moorings, and General Armstrong was directed, with the Pennsylvania militia, to guard the passes over that river. On the fifteenth the American army, intending to gain the left of the British, reached the Warren tavern, on the Lancaster road, twenty-three miles from Philadelphia. Intelligence was received early next morning that Howe was approaching in two columns. It being too late to reach the ground he had intended to occupy Washington resolved to meet and engage him in front. Both armies prepared with great alacrity for battle. The advanced parties had met, and were beginning to skirmish, when they were separated by a heavy rain, which, becoming more and more violent, rendered the retreat of the Americans a measure of absolute necessity. The inferiority of their arms never brought them into such imminent peril as on this occasion. Their gun-locks not being well secured, their muskets soon became unfit for use. Their cartridge-boxes had been so badly constructed as not to protect their ammunition from the tempest. Their cartridges were soon damaged, and this mischief was the more serious, because very many of the soldiers were without bayonets. The army being thus rendered unfit for action the design of giving battle was reluctantly abandoned by Washington and a retreat commenced. It was continued all the day and great part of the night, through a cold and most distressing rain and very deep roads. A few hours before day (September 17th), the troops halted at the Yellow Springs, where their arms and ammunition were examined, and the alarming fact was disclosed that scarcely a musket in a regiment could be discharged and scarcely one cartridge in a box was fit for use. This state of things suggested the precaution of moving to a still greater distance in order to refit their arms, obtain a fresh supply of ammunition, and revive the spirits of the army. Washington therefore retired to Warwick Furnace on the south branch of French creek, where ammunition and muskets might be obtained in time to dispute the passage of the Schuylkill and make yet another effort to save Philadelphia. The extreme severity of the weather had entirely stopped the British army. During two days Howe made no other movement than to unite his columns.