We heard that increased numbers were on the east side of Big Black. A party sent out yesterday, under one of my aides, went 10 miles beyond Bridgeport Ferry, and found the above statement correct. The regular patrol had quite a lively skirmish with some rebel force across the river, and, killed 1 man. The prisoners say that General Forrest, with 4,000 men, is in command across the river; their intended point of assembly in Mechanicsburg. At present (i. E., on the 12th) the cavalry was partly stationed at Bolton, Clinton, and on the Canton and Bridgeport road. Some were said to be at the above villages already. You undoubtedly admit the complexion of things makes the cavalry duty very hard indeed. The arrival of three small companies of the SECOND Illinois, under Major Marsh, did not bring much relief, and the early arrival of the remainder of Lieutenant Colonel Blush's command is, therefore, anxiously expected.

I am, colonel, with great respect, your most obedient servant,

P. J. OSTERHAUS,

Brigadier-General, commanding.

Lieutenant Colonel WALTER B. SCATES,

Assistant Adjutant-General.

HDQRS. NINTH DIVISION THIRTEENTH ARMY CORPS,
Big Black River Railroad Bridge, MISS., July 17, 1863.

COLONEL: Since my last report the complexion of things on my front has not changed. Rebel cavalry is appearing at every point permitting access on the eastern river bank, occasionally exchanging shots with my pickets. Yesterday a large force attempted to drive in the vedettes on the Edwards Station rad, but was readily repulsed by the reserve pickets. In general there, is no menacing attempt made as yet. This morning a very intelligent contraband George McCloud, came into our lines, who had left Demopolis, ala., on the 14th, Meridian on the 15th, and arrived in Jackson that same day. Yesterday morning he left Jackson for our lines. The negro was employed in the arsenal at Demopolis, and understands the making of all wood work connected with the ordnance department. He can read and write. This man states that the whole force at Jackson does not exceed 3,000 men, and the army collected and collecting by Johnston at Canton he heard estimated my leading officers at 15,000 effective meant at the outside, with no prospect to sell it beyond 20,000. He describes the people and soldiers, including officers, in very low spirits as to the success of the Southern cause. The theme of raising the siege of Vicksburg is freely discussed on all sides, but no hopes are entertained that their forces will be in condition or in number equal to meet the Federal army. Notwithstanding these of General Pemberton. Large quantifies of ammunition and ordnance stores were forwarded from Demopolis to General Johnston, and from the general run of conversation he thinks that an attack will be made within a very days on the right flank of our lines, with a view to give Pemberton a chance to break through the investing army. I will send the negro to your headquarters to-morrow morning, deeming him an interesting, perhaps a useful, and-perhaps a rogue. I had everything ready for the expected operator, when this morning some officer of another corps, passing Mount Alban with a squad of cavalry.