On March 1st, Senator Upham, of Vermont, introduced an amendment to the Senate bill, of the same tenor as the Wilmot proviso in the House, and urged its adoption in a strong and convincing argument. It really seemed as if the victory for Free-soil in the new acquisitions, whatever they might be, was about to be won, when, to the surprise of at least a considerable number of the Senators, General Cass, of Michigan, who was thought to have indicated his favor to the Wilmot proviso at the last session, made a determined effort against Mr. Upham's motion. Mr. Cass declared the measure premature, and contended that its only effect, if passed, at the moment would be to weaken the Government by internal dissensions upon the slavery question, and consequently encourage the Mexicans to continue the War. He urged the Senators to stand solidly together for the vigorous prosecution of the War to its successful close, and then, after the peace, take up the internal questions arising out of the settlement. The Senate rejected Mr. Upham's amendment, passed the bill without it, and, on the last day of the session, the House accepted the bill as it passed the Senate. Mr. Cass's idea that the anti-slavery proviso would embarrass the President in his negotiations with Mexico, and would {337} encourage the Mexicans to continue the War seems to have convinced the House as well as the Senate. [Illustration: CALIFORNIA AND NEW MEXICO in 1850.] The President had now the tacit consent of Congress to the acquisition of California and New Mexico, and the means to pay for them in hand. And the greater military successes of General Scott from Vera Cruz to the Mexican capital prepared the way for the President to make use of his power. [Sidenote: The mission of Mr. Trist.] The President sent Mr. N. P. Trist, of Virginia, to the head-quarters of General Scott with the draft of a treaty to be offered the Mexican Government. It designated the Rio Grande from the Gulf to the point where the River touched the line of New Mexico as the boundary between Mexico and the United States from the Gulf to that point, and provided for the cession of New Mexico and the Californias to the United States, and the privilege of the right of way across the Isthmus of Tehuantepec. Mr. Trist was instructed, however, that he might withdraw the demands for Lower California and for the right of way across the Isthmus, and might also offer a payment of money, if he should find these things necessary. [Sidenote: Rejection of Mr. Trist's propositions by the Mexicans.]