A correspondent of the Tribune gives the following account of the battle.

"Battle Field, Sunday, June 29, 1862, A.M.

A severe and most determined battle was fought on the right wing of the Army of the Potomac, on Thursday and Friday, the 26th and 27th instant, which is claimed by some of our officers as a successful strategic movement, into which the enemy have unwittingly been drawn, and which will soon result in the capture of Richmond as well as the entire army. "The attack was made by the enemy in immense force, who crossed the Chickahominy river, near the railroad, above Mechanicsville, on Thursday afternoon and fought desperately, but were unable to drive our men back a single rod from their position, notwithstanding we had to contend, in an unequal combat, with nearly or quite ten to one.

"The only forces engaged on that day, was McCall's Division, which was located on the opposite side of the swampy ravine, about a mile and a half back from the Chickahominy river.

"The battle lasted from about 2 until 9 P.M., when the enemy drew off, renewing the attack at the break of day, and after several hours of hard fighting, Gen. McCall's Division was ordered to fall back. The soldiers, supposing the order was given from the fear of being over powered, said they could hold the ground, and begged that the order might be countermanded, which was refused, and they yielded with great reluctance.

"General McClellan was on the field during the afternoon and up to a late hour at night, directing the movements, and expressed himself well satisfied with the result.

"On Friday morning commenced what is called the "strategic movement", which, it is hoped, will be a success although at one time nearly proved fatal, to a considerable portion of our army.

"Below I give the facts of the two days' battle, as gathered by personal observation, and from various other sources, but which, as is always, the case while the battle is raging or immediately after, are imperfect, in consequence of the conflicting statements of persons located at different points of the field operations."

The Rebels Attack on Thursday

"On Thursday, about noon, the enemy made an attack upon Gen. Stoneman's forces in the vicinity of Hanover Court House, probably for the purpose of accomplishing an out-flanking movement on the right, and to engage our attention in that direction. Shortly afterwards they commenced a vigor cannonading from the works situated on an eminence opposite Mechanicsville, about one and mile distant; also from two batteries, one above and the other below.

"They were replied to by Campbell's Pennsylvania batteries on picket duty, one on the Mechanicsville road, and another from behind earthworks at the right of the grove."

The Rebels Cross the Chickahominy

"About 2 P.M. the enemy's infantry and squadrons of cavalry crossed the Chickahominy in immense force, a short distance above the Virginia Central Railroad, making a rapid advance, through lowlands and forests, towards Gen. McCall's Division, were entrenched on a hilly woodland across a swampy ravine, about a mile and a half in the rear of Mechanicsville."

Part of the Pennsylvania Bucktails Captured

"The First Pennsylvania Rifles (Bucktails) and Campbell's Pennsylvania battery were on picket duty, all of them, except one company, fell back behind the breastworks and rifle-pits, where a line of battle was drawn up. Company K, of the Bucktails, who were on picket beyond the railroad, were surrounded by the enemy, and the last that was known of them they were trying to cut their way through an immensely superior force. Their fate is not known, but it is presumed that the greater portion of them were taken prisoners."

A Terrible Conflict

"The enemy advanced down at the rear of Mechanicsville, on a low marshy ground, to where our forces were drawn up behind rifle-pits and earthworks, on an eminence on the northerly side of the ravine, when the conflict became most terrible. The Rebels, with the most determined courage, attempted to press forward over miry ground but the bullets and grapeshot fell among them like hail, until, in the words of an officer, "they lay like flies on a bowl of sugar," and at dark withdrew. The cannonading was kept up on both sides until about nine P.M., when the battle ceased. Our forces were covered by earthworks, and suffered but slightly. The casualities, as far as known, are given below.

"Late in the afternoon the enemy made a charge with cavalry. About one hundred of them came rushing down and attempted to cross the ravine when the horses became mired. A squadron of our cavalry, seeing the position in which the enemy were placed, made a charge down the hill, when the cavalry abandoned their horses and fled.

"The infantry fight was then renewed, and according to the statement of my informant, Surgeon Humphrey of the Bucktail regiment, continued until about seven P.M., when a retreat was ordered, very much against the will of the Pennsylvania boys, who begged to be allowed to defend their position, which they felt confident they would continue to hold "The cuter forces began to fall back. Porter's Corps were some distance below, near what is well known here as Dr. Gaines' residence.

Retreat of Our Right Wing

"At the break of day I turned out from my comfortable bed (the ground) after the fight of the day before, for the right wing, where they had been an incessant cannonading for sometime.

"The first that attracted my attention was the immense line of baggage and forage wagons, extending about four miles. Next came a cavaleade of ambulance wagons, extending as far as the eye could reach, and on the next eminence the view was charged.

"Next came stragglers, who never happen to be under fire, but can report hair breadth escapes and personal adventures, with the final tale that "our regiment is all cut up, and only about two hundred and fifty of us left." Next came along the sick soldiers on foot, and lastly, a negro, dragging one foot after another, apparently much frightened, and a soldier by his side damning him for not moving faster.

"A moment after we decended the hill to a ravine know as Gaines' Mills, and halted for an artillery battery which was hurriedly crossing the bridge, and as the last train passed over, an order was given to destroy it. At this moment a depleted regiment came over the eminence, and seeing the work of destruction going on, cried out, "stop, stop, the enemy are close upon us," some of them at the same time glancing backward.

"Your, correspondent had started out breakfastless for Mechanicsville, but suddenly became impressed that he had some business in an opposite direction. Returning about two miles, he came into an open space of rolling land about one and three-quarters miles in length, extending to Woodbury's Bridge, across the Chickohominy, and the remainder high rolling land skirted with woods.

"Previous to reaching the open space, skirmishers were being thrown out, and their actions would lead one inclined to timidity to suspect the enemy had crept up uncomfortably near.

"Passing to the open space we saw an immense force; some drawn up in line of battle, and others marching and countermarching. These consisting of Porter's Corps and McCall's Pennsylvania boys who had yielded against their will."

The Second Day's Battle

"Two hours afterward the enemy came feeling their way through the woods, and finally a general battle ensued. The cannonading was terrific, and the musketry can only be understood by those who have heard the crash of immense trees in quick succession.

"Duryea's gallant Zoueves were laying on the ground for two hours, while our batteries were shelling the woods over them.

"Finally toward night, the enemy attempted to break the entire line in front of Duryea's Zouaves, and the musketry firing became most terrific, lasting some twenty of thirty minutes, after which there was a lull. Shortly afterward an attempt was made to break through the right, which was repulsed, and half an hour later another attempt was made on the left, with the same result. The battle had been raging for some hours without any apparent change or advantage on either side.

"Reinforcements of artillery and infantry then came steadily along over the bridge, marching through the heat and dust over the hill to the field of battle. The enemy then seemed to make their last desperate, determined effort, and came near forcing our men back into the low ground between the hill and the bridge, where they could have been slaughtered by tens of thousands before they could have crossed that long, narrow bridge. Wagons, artillery, ambulances and men were hurrying towards the bridge, and a panic was most inevitable, when a strong guard was placed across the bridge."

The Irish Brigade Strip to Their Work

"At the time when the enemy had almost reached the main hospital one half mile from the river, Thomas Francis Meagher's Irishmen came over the hill stripped to their bare arms, and ordered to go to work. They gave a yell and went to work, and the result was that the enemy fell back to the woods, and thus matters stood up to eleven o'clock yesterday (Sunday) morning.

"At dark an attack was made along the entire line, and was renewed at 2 a.m. in front of General Hooker, Kearney and Sumner, successively, without material result."

Our Losses

"Colonel Black of Pennsylvania, was killed, his head blown off by a shell. When we lost Easton's battery we lost its valuable commander beside. Ten guns were taken from us by a sudden flank attack, covered by the thick smoke that hung around the pieces and slowly drifted to leeward."

Statement of a Rebel Major

"Count de Paris took prisoner a Rebel Major, who belonged to Jackson's army. He said he had been in the valley of the Shenandoah all winter and came here yesterday with part of Jackson's army. The rest arrived this morning. The whole of it was here. He said in the attack on our right the Rebels had from sixty thousand to eighty thousand troops. This will explain the enormous fire under which our men were borne down and swept away, precisely as some of the regiments were swept away at Seven Pines.

Incidents

"The Pennsylvania Reserve drove the attacking regiments of Jackson's command. To-day they were overpowered by the same troops, reinforced. Sykes's Regulars, called up, proved unequal to the task of stopping them. The Count de Paris testifies to the remarkable good conduct of all the regiments that sustained this unequal attack on Porter's. They gave way, indeed, but none of them ran. Their losses are enormous. "The regular Eleventh Infantry is about annihilated. Nearly every officer in it is killed or wounded. The Fourteenth also suffered severely. Major Roselle, of the Regulars, a kinsman of General McClellan's is killed. Colonel Pratt of a New York regiment, is also killed, and Lieutenant-Colonels Black and Sweitzer.

"Our loss in officers is very marked. Indeed the disproportion in numbers was so extraordinary, the obstinacy of our troops so unyielding, that our losses were unevitably large. The artillery in both Porter's and Smith's piled the rebels in heaps. The fire was horribly effective. "At Savage's Station the wounded already fill the great street of tents in the garden, and begin to pave the grass yard as after the Seven Pines. The same moaning and shrieking fill the night as then, and again bear testimony against the stile of warfare which submits to the fire of brigades."

Summing Up

"This fight to-day (Friday) cannot be described, save by a memorandum of the positions respectively held by opposing parties at its close, and by the list of killed and wounded. On the Rebel side, however, it was characterized by the steadfast old policy for which their leaders are to be so much honored, of pouring in fresh and eager troops upon our weary men, and endeavoring to crush us with superior weight of fire and vastly superior exhibition of force.

"Twice, all along the front, did the bloody and determined attack cling to our lines of battle and our rifle-pits, and redoubts. Porter thundered on them with fifty cannon; Sumner's, Hooker's and Ayers' loss in killed [and] wounded was horrible. We but debate now if our dead, wounded and missing equal those of the Seven Pines--or, exceed theirs!! In the meantime, notwithstanding the disproportion of numbers, the Union line is at every point about where it was in the morning, and the heroes behind it are in heart."