_Sunday, August 30._--To-day I accompanied the division and brigade officers of the day in their visit to and inspection of the pickets along the Rappahannock. Our ride was very pleasant. Captain Barker, of the Fifth New York Cavalry, dined with Captain Mitchell and myself. He is a lively companion; was in the hands of Mosby last Spring; and has a fund of amusing and interesting incidents of army-life with which to enliven his conversation. On the last day of August, Captain Mitchell was ordered to report to the regiment at Hartwood Church, with his reserves. The pickets are to remain on the river until attacked by the enemy or recalled by orders from division headquarters. CAVALRY GUNBOAT EXPEDITION. _September 4._--To break the monotony of picketing and to subserve the cause of freedom, a most novel scheme was lately undertaken, known as Kilpatrick's Gunboat Expedition. The object was to destroy a portion of the Rebel navy anchored in the Rappahannock, near Port Conway, opposite Port Royal. This peculiar kind of warfare, which required genius and dash, was waged by the troopers with complete success, and they returned to their bivouac fires to enliven the weary hours with stories of their long march down the river, and their destructive charge upon the gunboats of the enemy. The expedition set out about two o'clock on the morning of September first. Doctor Lucius P. Woods, Surgeon-in-Chief of the First Brigade, Third Division, gives the following interesting description of the above raid in a letter to Mrs. Woods: "I returned yesterday after a three days' expedition after gunboats! We all laughed at the order sending cavalry after such craft, but I am happy to say that the object of the expedition was accomplished. We left camp at two o'clock A. M., marched all day and all the following night, till three o'clock next morning, when we made a furious charge upon Rebel infantry. They ran so fast as to disarrange the general's plan of attack. The morning was so dark that we could not see one rod in advance.