Returning, however, to our picturesque camp in this charming valley. There was no more striking scene than when darkness came on and the thousand camp fires and lights in the tents were all in sight. The rail fences, bought by the thoughtful quartermaster, and paid for as an army supply, were used as fuel; a truly considerate act, for a quartermaster can buy fuel for the army, but he cannot pay damages done to property. This same ground, now covered by our troops, had been camped over by Lee's army; who had also used the fences, not even paying for them in the worthless Confederate scrip. Soon after dark, the bright lights of the signal corps appeared on the mountain north of the Maryland Heights, and messages were sent to McClellan's headquarters. Flags are used in the day, and at night lanterns. The signal officer has two lights; they are held one above the other, the lower one being stationary; moving the upper light to the right means number one; moving the light to the left, number two; moving first to the right and then to the left, number three; by lowering the upper light in front of the under one, a fourth signal is given; and so on. There are about five numbers; and by the different combinations of these five numbers, there is made a great number of signals, which can be read by the officers who have the key. The mode is much the same as that used by our mercantile marine with their signal flags. The signals are given very rapidly, and a few minutes suffice for the sending of the messages.