Northern Senators and Representatives, in the face of the overwhelming public sentiment of the North, expressed in the proceedings of public meetings and solemn remonstrances, without a single petition in its favor on their table, and not daring to submit this great question to the people, have yielded to the seductions of executive patronage, and, Judas-like, betrayed the cause of liberty; while the South, inspired by a dominant and grasping ambition, has, without distinction of party, and with a unanimity almost entire, deliberately trampled under foot the solemn compact entered into in the midst of a crisis threatening to the peace of the Union, sanctioned by the greatest names of our history, and the binding force of which has, for a period of more than thirty years, been recognized and declared by numerous acts of legislation. Such an outrage upon liberty, such a violation of plighted faith, cannot be submitted to. This great wrong must be righted, or there is no longer a North in the councils of the nation. The extension of slavery, under the folds of the American flag, is a stigma upon liberty. The indefinite increase of slave representation in Congress is destructive to that equality between freemen which is essential to the permanency of the Union. The safety of the Union--the rights of the North--the interests of free labor--the destiny of a vast territory and its untold millions for all coming time--and finally, the high aspirations of humanity for universal freedom, all are involved in the issue forced upon the country by the slave power and its plastic Northern tools. In view, therefore, of the recent action of Congress upon this subject, and the evident designs of the slave power to attempt still further aggressions upon freedom--we invite all our fellow citizens, without reference to former political associations, who think that the time has arrived for a _union_ at the North to protect liberty from being overthrown and down-trodden, to assemble in mass convention on Thursday, the 6th of July next, at 4 o'clock, P. M., at Jackson, there to take such measures as shall be thought best to concentrate the popular sentiment of this State against the aggression of the slave power.