Our local reporters give this morning an account of one of the most atrocious riots of modern times, which occurred in Brooklyn yesterday, and in which a mob of four or five hundred men, calling themselves Irishmen, assaulted a factory where twenty peaceable colored persons, mostly women and children were at work, attempted to butcher them in cold blood, and subsequently actually set fire to the building with the intent of burning the helpless negroes to death. It was only by the most superhuman exertions of the Police that the lives of the victims were saved, the mob dispersed, and the ringleaders arrested. The assault was entirely unprovoked -- in fact, it was merely because the assaulted parties were negroes -- and was of such a cowardly as well as fiendish nature that there can be found for it neither excuse nor palliation.

What do these ruffians want -- what object have they in view -- who are stirring up anti-negro riots in various large cities of the North? Do they think to aid the cause of JEFF. DAVIS, by diverting part of the National strength for the preservation of order at home? Are they the tools of the Northern rebel knaves and conspirators who, having failed in getting up that counter-revolution in the North which the Southern rebels hoped for and had planned, are now taking hold of their social and National prejudices, and through them, stirring them up to sedition? Do they desire, to justify the taunts of the English Press as to our Northern anarchy and our Northern mobs? Do they wish to deprive these harmless black pariahs of the means of obtaining and honest livelihood? Is their object to disgrace themselves and belie their national reputation by acts of poltroonery too disgraceful for record? All these things, and worse too, are the tendencies of such mobs as that in Brooklyn yesterday.

There is no class of persons in this community more quiet, orderly, peaceable, respectful, and even courteous, than the colored people. Their habits of industry are, as a general thing, and considering their opportunities highly creditable; the annals of crime show that neither among the foreign nor native born white citizens, is there any class of nationality as free from offences against the laws; and though here, as elsewhere through out the world, the struggle for life is will them a hard one, they bear their burdens with a patience which none but a brute could take advantage of -- none but a devil could insult them for. The present riots, neither here not in Cincinnati, nor anywhere throughout the West that they have occurred, can find any excuse whatever in the character of the negroes.

We are glad that this, our first anti-negro riot was put down so quickly and effectively -- though it is disgraceful to the Brooklyn Police that it should ever have occurred, or attained to such proportions, or effected such damage. It is no time now for any mob, of show of mobs, in any part of the North, under any pretext whatever. They are more disgraceful than the Southern rebellion, and the ringleaders deserve the doom of traitors while their dupes should all be drafted into the army, where they will find a kind of fighting more creditable to themselves than assaults upon unoffending and helpless women and children. We understand that some of the rioters are still at large; but we trust the police will see to it that before night every one of them is safe in limbo. There must be no tampering with this matter. It is safer and easier to crush it out now and at once, in its inception, than to try to put the riots down after they have attained such magnitude and persistency as they have done in Cincinnati. Let the police be alert and on their guard. Let every man and class of men, white or black, be protected in their avocations, and in the secure and unmolested enjoyment of "life, liberty and the pursuit of happiness."