The letter of President Lincoln to General MeClellaD, dated April 9th, 18G2, wliich was produced on the McDowell Court of Inquiry yesterday, will attract widespread attention. It sets at rest many vexed questions, and among others the following : 1. That President Lineoln real'y did interferc with the plans of Gen. McClellan by keeping Gen. MeDowell's corps on ihe "Rappahannock after it had been ordered to the Península by the General eommanding. 2. That President Lincoln urged Gen McCIellan to " move upou the enemy's works" at Yorktown, as Gen. Burnside subsejuently did at Fredericksburg 3. That Gen. McClellan's total forco, when he lur.ded on the l'eninsula, was only 85,000, which is rather a falling off as cornpared with the magnifieent figures of Chandler's speech, This Presidential interference with Gen. McClellan's plans, which began with the debarkation of the troops for Fortress Monroe, tells the whole story of the mis c;rmge, uot only of the Península, but of all the other campaignss against Kichmond.