Having thrice visited Texas, and traversed nearly the whole State, north, south, east, and west, I speak from personal knowledge. In one county, I observed first rate wheat, cotton, and sugar cane growing in adjacent fields, and the soil and climate well adapted for all three crops. In Texas, the product of wheat has increased from 41.79 bushels in 1850, to 1,464,273 bushels in 1860, and the number of bales of cotton from 58,072 in 1850, to 405,100 bales in 1860, far exceeding the rate of increase in any other State. (See table of Census, No. 36, pp. 200, 210.) Having very nearly six times the area of New York, Texas, when cultivated by free labor, can produce cotton enough to clothe the people of the world, and supply all Europe with wheat also. The rapid colonization of Texas by freemen ought to add to our wealth, in this decade, a sum equal to the present debt of the United States, and terminate in our favor the effort to supplant us in the supply of cotton for the world. The isothermals of the great Humboldt (differing so widely from parallels), which trace the lines of temperature on the earth's surface, prove, as to heat, the climate of the South (running a line from Charleston to Vicksburg) to be substantially the same as that of Greece and Italy--each, in its turn, the mistress of the world. I know, when, the term _isothermal_ was used in my inaugural as Governor of Kansas, it was represented by some of our present rebel leaders, to the masses of the South, as some terrible monster, perhaps the Yankee sea serpent; but I now use the term again in no offence, from its important application to the present case, and knowing that what I now advise would produce incalculable benefits to the whole country, but especially to the South. Indeed, if Texas, with her 274,356 square miles of area, with her salubrious climate, and fertile soil, already worked to a great extent by free labor, were a free State, she would, in time, contain a larger population than any State of the Union. Texas has much more than five times the area of England proper, and, with the same population to the square mile, would contain more than one hundred millions of people. Having, in 1837, offered in the Senate of the United States, and carried, the resolution, recognizing the independence of Texas, first proposing in my letter of the 8th January, 1844, the mode, by _compact_ (alone practicable), by which, on my motion, Texas was admitted into the Union, distinctly advocating, in this letter, the reannexation of Texas, with, a view to secure the ultimate disappearance of slavery and negroism from the whole country, in opposition to the object officially avowed by Mr. Calhoun, to annex Texas for the purpose of perpetuating slavery, I shall, in a future letter, discuss this subject, involving not only our furnishing a certain abundant supply of cheap cotton, but securing the real monopoly of this great product, due to our _peculiar_