At all times since the traitors commenced their war upon the Government, they have misrepresented to foreign nations their true purpose, knowing full well that if they boldly announced that they were fighting in behalf of the vilest system of oppression and slavery, instead of receiving aid and sympathy they would excite the universal scorn and horror of mankind. So the Yanceys and the Rosts and other advocates of the Southern cause in Europe, ashamed to admit the truth, have labored to deceive the people there, by attempting to show that they rebelled in consequence of high tarifs imposed by the North. That meanest of all traitors, Lieut. Maury, has lately been trying his hand at falsehood by writting a letter addressed to the Admiral in the French Navy, which is reprinted in the London Herald. Here is what he says about the cause of the rebellion :