Mr. Emil Schalk, author of a work on . the present campaign, has commu,nieated the following opinioa to the Philadelphia Press : Sir - When battles are fought in which thousands and thousmids of brave soldiers are iminolated, but which, notwithstauding the great sacrifica, do not obtain an adequate resul t for the enormous lo.s of life, is it theu not the duty of every í'riend of the country to inquire into the cause of the disasters which cover a whole nation with niourning, and which, in its history remuius a dark spot in its glory ? The lote battle of Predericksburg and Chancellorsville, with its hecatombs of human beings, may, like nearly all other lost battles of this war, be traeed directly to the mistakes of thfi generáis commanding, and it is but just that the whole country should have a clear insight into those mistakes, for it may bo that thus more errors in future will be avoided. Looking at tho map it will be seen tbat the rebel army, in its oncanipments noar Fredericksburg, held' a line running from northwest to southeast; its right wing was extended'as far down as Port lloyal, on the llappahannock ; its left wing rosted above Eredoricksburg, on the same river. This army has only two lines of retreat - one toward Richmond, the other towards Gordousville. It cannot retreat to the east or southeast, as such a mareh would carry it into the Potomac or York Rivcrs. Under these cireumstances tho natural point of attack is the rebel left wing. - If this wing is seriously defeated, and the victory rapidly followed up, the rebel army would be pressed from its two lines of retreat agamst the south-cast ; thrown agairist the rivers, it would finally be obliged to surronder, the samefate whiuh -befell the Prussian army after the battle of Jena. Crossing, thorefore, abovo Frederieksburg, at United States Ford, for instance, marohing rapidly to Clianeellorsville, and from there to a point midway between Canecllorsville and Guiney, on i the railroad (or if the last move be eon! sidered too daring, moving straight from Ohaneellorsvilie against Fredericksburg), would be the correct strategical move to obtaÏD the desired result, viz : the desIruotion of the rebel army. Utmost speed, conceutratiou of force, and utmost daring would guaranteo complete success. Oen. Hooker arranged his plans of atiac-k as follows.: Ho had seven army corps; of theec threc were massed below Fredericksburg, to cross there and make a feint attack on tho rebels, two of the corps, imniediatcly after the crossinir, to return and join General Hooker, who meanwhile was crossing with the four remaining corps at several fords, some ten to Iwenty miles above Fredericküburg. On Sundiiy, April 2G, tho movement was commenced ; on Monday it was continued, and on Tuesday morning the : threo corps below Fredericksburg, and i on Tuesday night and Wednesday morning the four corps above Fredericksburg I made goed their croesiug. On Wednesday and Thursday the main army raoved to Chancollorsville, sonie five milíís from the principal crossiug place, making five miles iu t.liirty six hours. Friday was oecupied by throwing up iutrenohiuonts; Saturday the figliting scriously commenced ; Saturday eveuing only, as it appears, the two remaining corps arrived from below. Suuday another attack and repulse of the main army. Meanwhile Sedgwick carries the intrenchmentsbehiud Fredericksburg. By Sedgwick's movcmcut two lines of operatious are clearly formed- tlie two Unioo armies separated by a distance of twenty miles, the rebels in a central positiou between them. While all these mo vemen ta are beiug carried out the whole cavalry under General Stoneman is detached on a raid ia the rear of the rebel army. Gen. Lee, without heedhig the cavalry in his rear, waits quietly in his intrenchments till the Union movement is fully developed. He easily discerns the feïnt from the real attack. He throws his 'whole force against General Hooker, whom he confronts on Thursday ovening, giviug up, mcnnwhüc, his intrenchments near Predsricksburg, Hooker is beaten on Saturday. On Sunday, seareely is he on ihe defensivo when Gen. Lee, by means of his interior line of íbices, marches Sunday night, and throws, on Monday, the mass of his forces against Sedgvvtck, wlio the day before had carried the fortifieatioas near ■Fredericksburg. Sedgwick is beaten, crippled, and scarcely escapes annihila tiou. After this triple check General Hooker gives up the contest, and recrosses the river. By wLat we have said above of the position of the rebel army, it will bc seen that the crossiug at Chancellorsville by the maiu fores, was ontirely correct; but it will be seen, too, that the crossiug effected by four .corps only, instead of seven, or at least six, was entirely incorrect Had the army consisted of the seven corps, and marched on Wednesday ïnorning, in forced marches towards Frodoricksburg, or in a divection some five to six miles south of Fredericksburg, they would have been, by Wednesday night, behind the rebel intrenchments. The Great decisive battle of the war would probably have taken place on Thursday, and would have been fought under very diifcrent eircurustances from those of Saturday, Sunday and Monday, where our army was beaten in detail. The idea of a general, icho is on the offensive, wltose avoioed olject is the capturV ■r destniction of a wwle army, making six miles in thirty six hours, ju&t at the most ïritical mom-nt of his operations ; and ünally, after intrenching himself without being on the communwations (f his enemy, (elk his soïdiers thal the enemy has to run iway or to attack him on his own ground where he will destroy hun, has not lts parallel in modern times. Another quite as unpardonablo mistake is the sending away of the cavalry in a moment when a great battle was nearly certain to happen. It was the same süly condnat which made Melas lose the batttlo of Marengo. The cavalry ought to have formed the utmost rjglit wing in the large wheeling movement whioh our army performed and in which the left wing formed the pivot. General Hooker's operation is modeled on the operations of Wurmser and Alvinci, in 1796, in Italy; thoso of Jour dan. 1799, at iStokach; and, in quite modern times, on that of the royal Neapolita-3 army, in 1860, at the Nolturno. On the contrary, Gen. Leo took a good lesson from the action of Napolenu, the Archduke Charles and Garibalili, on these different occasions. Gen Lee has eertainly gained for himself, by this battle, the name of 'one of the ablest Generáis of the present age. Tt would be wrong to make General Hookcr alone responsible for his defeat. Wc are told that his army is to be reinforced by thirty thousand men from Washington, and by foi ty thousand to fifty thousand from Suffolk Is it not strangc that these troops did not join Hooker before the battle ? What is the use of thirty thousand idle men in Washington ? What is the use of these fifty thousand in the Blaekwater ? Why are some twonty thousand standing sentry in North Carolina? What have the thirty thousand done yet near Charleston ? Is there not ccmmon sense ennugh in our grcit Generáis to understand that to keep thousamls of' inen as sentries to prevent blockade runners from co.ring in to Southern ports is ridiculous: that it is more reasonable to mass all those h'oops, and to crush with this supenority the encmy's niain anuies, beeause then the blockade runners will soon find no more buyers for their goods? But how could sueh reasonable action be expected from a Góncral-in-Chief who advaneed against Cörinth with a sruiillike pace to undertake the siege of fieldworks whioh the rebels aficrwards, undcr Van Dorn, did not hesitate a tnonient to storm ; and who sent Pope with 30,000 men to capture an army which he, with 100,000 could not defeat? It is the same General who, in August last, gave General Burnside the strange order to stay quietly t Frederieksburg with his troops; meanwhilc Pope was defeated ut Manassas. 1 he siune who ordered Pope to rctrent toward Washing ton instead of ordering him to retreat toward3 Salem and Berlín, whieh would have prevented tlie battle at Manassaa and the invasión of Maryhind. It is the same who gave the fatal order to Colonel Miles to hold Harper's Ferry when the rebels were already in Waryland, and when therefore Harper's Ferry had lost all importance. Have there not been useless buteheries and faihiïcs of operations enough to warrant fioally the adoptiou of ouud tary plans? Till this is done, we can only hope that fortune will once more smüü upon the country of freedom. I ani, sir, yours, vcry truly, É. SCHALK.