PITTSBURGH, January 28, 1848.

DEAR DOUGLASS:—Since I last wrote, nothing of interest has transpired. Anti-Slavery seems to be at a low ebb in this county; at least if present appearances are a test of the reality. We cannot get up a meeting of any considerable number here; nevertheless, the true and real friends of the slave stand firmly to their integrity. Of such, there are many here, voters and non-voters; (but few of the latter, and many of the former;) and strange and paradoxical as it may appear, though the friends of the cause are many, the cause itself suffers much.

There is, as you know, quite a liberal feeling in this community; but the truth of the matter is, that every man is such a real slave to his own business, that he has not time to devote to the suffering slave to man.

Another influence appears to bear against the cause of Anti-Slavery in this region.—The Mississippi valley and its connecting rivers, are but the train of communication, or the great telegraphic medium which binds Pittsburgh, New Orleans and St. Louis together in interest; merchants here, being interested in trade, vessels and shipping houses there; families here being intermarried and consanguineously allied to families there, until they have, although, in themselves, essentially three, become one. They doubtless now look upon themselves as one in three; hence the absence of Anti-Slavery action in Pittsburgh and Alleghany Co.

The Legislature of Pennsylvania, although not as yet sufficiently enlightened to recommend an alteration of the Constitution, so as to amend the odious third clause, are beginning to exhibit germs of civilization, by talking about the death penalty, &c. But while this is going on, faithful to the biddings of the South, some one of their numbers has introduced a bill to prohibit a panting fugitive from setting in Pennsylvania.

The scheme, now freely and openly discussed, concerning the incorporation of Mexico with the United States, is a project the most frightful and monstrous within the pale of human conception. And even Dr. Bailey, of the Era, and some others who call themselves Abolitionists, favor and contend for a consummation of this project. They argue that it will facilitate the overthrow of American Slavery, and forsooth, bring the Mexicans under a more settled and stable government.

But what are the facts in the case? But a glance will suffice to show the fallacy and duplicity of this whole nefarious scheme.

Mexico is people by ten millions of inhabitants; but fifteen hundred thousand, or three-twentieths of whom are whites, the rest, seventeen-twentieths, or seven and a half millions, are Indians and mixed colors—from the black to the fairest quadroon. According to the Christian usages, laws and customs of this free republic, no colored person—that is to say, black, mulatto, or Indian—is eligible to the privileges secured to and enjoyed by the whites. Such being the case, should this high-handed project succeed, while it might in reality speed the overthrow of slavery, as such, in the South, yet in doing so, would bring with it degradation and servility to nearly eight millions of freemen, heretofore enjoying the rights and privileges of a free and equal people, common to all, of whatever origin; while but one and a half million would retain those rights, enjoyed in common heretofore by all! And this is what we are asked to subscribe to! How superlatively devilish is this whole scheme! Nay, rather than this, let all Mexico be engulfed in the horrors of an earthquake!

President Polk is proving himself an absolute monarch, by his peremptory refusal to obey the National Legislature. But this is all right. Let the slaveocrats go on, and the pro-slaveocrats at the North will learn, when too late, their most egregious error, in having "nothing to do with slavery."

Colored People! we want more business men among us; farmers, mechanics and tradesmen. We must, in order to be respected and gain our lost rights and privileges, use the means necessary and adequate to the accomplishment of such a desirable end. Let our people put their children—first to school, next to trades. This must be done.

The North Star comes, to the pleasure and approbation of all who receive it. I am receiving many letters from the West, in which it is hailed as a great beacon-light, wherever it has cast its refulgence. I hope soon to be on my Western tour, and wish you to say to our Western friends, that they may all be prepared for subscription, as I shall give them a general visit. I shall hold at least one meeting every place I go, if I can get an audience, although I shall make my stay very short in each place. I omitted to mention in my former correspondence, that the cause of my long silence was owing to indisposition in my family, at which time I am little prepared for writing, especially when fatigued,at the bedside of a tender and interesting child. You shall hear from me soon again.

Yours, in behalf of our oppressed and down-trodden countrymen,

M. R. D.