The relative progress of Maryland has been slow indeed. The population of the Union, by the census of 1790, was 3,929,827, of which Maryland, containing then 319,728, constituted a twelfth part (12.29). In 1860, the Union numbered 31,445,080, and Maryland 687,034, constituting a forty-fifth part (45.76). In 1790, the free States numbered 1,968,455, Maryland's population then being equal to one sixth (6.12); but, in 1860, the population of the free States was 18,920,078, Maryland's number then being equal to one twenty-seventh part (27.52). But, if Maryland had increased as rapidly from 1790 to 1860 as the whole Union, her proportion, one twelfth part, would have made her numbers in 1860, 2,620,315; and if her proportional increase had equalled that of the free States, her ratio, one sixth, would have made her population in 1860, 3,153,392. She might not have reached either of these results; but, before closing these articles, it will be proved that, in the absence of slavery, her population, in 1860, would have been at least 1,755,661, or the same per square mile as Massachusetts; and Baltimore, bearing the same ratio to this number as to Maryland's present population, would have contained in 1860, 542,000, instead of 212,000, her present number.

I take the areas from the able report (November 29, 1860) of the Hon. Joseph S. Wilson, then Commissioner of the General Land Office, where they are for the first time accurately given, 'excluding the water surface.' The population is taken from the census, the tables of 1850 and 1860 being compiled with great ability, by the present superintendent, the Hon. J. C. G. Kennedy. I compare first Massachusetts and Maryland, because they are maritime and old States, and both in 1790 had nearly the same population, but, as will be shown hereafter, with vastly superior natural advantages in favor of Maryland.

Area of Maryland, 11,124 square miles; shore line, by tables of United States Coast Survey, viz.: main shore, including bays, sounds, &c., 503 miles, islands 298, rivers to head of tide water 535; total, 1,336 miles.

Area of Massachusetts, 7,800 square miles; shore lines, by tables of United States Coast Survey, viz.: main shore, including bays, sounds, &c., 435 miles, islands 259, rivers to head of tide water 70; total, 764 miles. When we mark the Potomac and its tributaries, the lower Susquehanna, the deep and numerous streams of the Chesapeake, the commercial advantages of Maryland over Massachusetts are vast indeed. Looking at the ocean shore of Maryland, and also at the Chesapeake bay, the largest and finest estuary in the world, indented with numerous sounds and navigable inlets, three fourths of its length for both shores being within Maryland, and compare this deep and tranquil and protected basin, almost one continuous harbor, with the rock-bound coast of Massachusetts, lashed by the stormy Atlantic, the superiority of Maryland is striking.

Mortality in Maryland, by the late census, viz.: deaths from 1st June, 1859, to 31st May, 1860, 7,370 persons. Same time in Massachusetts, 21,303; making the ratio of deaths to the number living in Maryland, one to every 92, and in Massachusetts one to every 57; and the percentage of deaths in Maryland 1.09, and in Massachusetts 1.76. This rate of mortality for Massachusetts is confirmed by the late official report of their Secretary of State to the Legislature.

As to area, then, Maryland exceeds Massachusetts 43 per cent.; as to the shore line, that of Maryland is nearly double that of Massachusetts, having 68 miles more of main shore, bays, and sounds, 38 miles more for islands, and nearly eight times the number of miles for rivers to head of tide water. As to climate, that of Maryland, we have seen, is far the most salubrious. This is a vast advantage, not only in augmented wealth and numbers, from fewer deaths, but also as attracting capital and immigration. This milder and more salubrious climate gives to Maryland longer periods for sowing, working, and harvesting crops, a more genial sun, larger products, and better and longer crop seasons, great advantages for stock, especially in winter, decreased consumption of fuel, a greater period for the use of hydraulic power, and of canals and navigable streams. The area of Maryland fit for profitable culture is more than double that of Massachusetts, the soil much more fertile, its mines of coal and iron, with the fluxes all adjacent, rich and inexhaustible; whereas Massachusetts has no coal, and no valuable mines of iron or fluxes. When we reflect that coal and iron are the great elements of modern progress, and build up mighty empires, this advantage of Maryland over Massachusetts is almost incalculable. The hydraulic power of Maryland also greatly exceeds that of Massachusetts. Such are the vast natural advantages of Maryland over Massachusetts. Now let us observe the results. Population of Maryland in 1790, 319,728; in 1860, 687,034; increase 367,300. Population of Massachusetts in 1790, 378,717; in 1860, 1,231,065—increase 852,348; difference of increase in favor of Massachusetts, 485,048; excess of Massachusetts over Maryland in 1790, 58,989, and in 1860, 544,031. This result is amazing, when we regard the far greater area of Maryland and her other vast natural advantages. The population of Maryland in 1790 was 28 to the square mile (28.74), and in 1860, 61 to the square mile (61.76); whereas Massachusetts had 48 to the square mile in 1790 (48.55), and 157 to the square mile in 1860 (157.82). Thus Massachusetts had only 20 more to the square mile in 1790, and 96 more to the square mile in 1860. But if the areas of Maryland and Massachusetts had been reversed, Massachusetts, with the area of Maryland, and the population of Massachusetts of 1860 to the square mile, would have numbered then 1,755,661, and Maryland, with the area of Massachusetts and the population of Maryland of 1860 to the square mile, would have had then a population of only 481,728 upon that basis, leaving Massachusetts in 1860, 1,273,393 more people than Maryland. Thus is the assertion in a former part of this article now proved, 'that in the absence of slavery, the population of Maryland in 1860 would have then been at least 1,755,661, and Baltimore at least 542,000.' But, in view of the many other natural advantages of Maryland, as shown in this article, viz.: in climate and salubrity, in shore line and navigable rivers, in fertility of soil, and hydraulic power, in a more central location for trade with the whole Union, and especially with the West, and nearer supplies of cotton, and, above all, in coal and iron, it is clear, in the absence of slavery, Maryland must have contained in 1860 a population of at least two millions. By the census of 1790, Massachusetts was the fourth in population of all the States, and Maryland the sixth; but in 1860, Massachusetts was the seventh, and Maryland the nineteenth; and if each of the thirty-four States increases in the same ratio from 1860 to 1870, as from 1850 to 1860, Maryland will be only the twenty-fifth State.

These facts all conclusively attest the terrible effects of slavery on Maryland, and this is only one of the dreadful sacrifices she has made in retaining the institution. As to wealth, power, and intellectual development, the loss cannot be overstated.

Nor can manufactures account for the difference, as shown by the still greater increase of the agricultural North-West. Besides, Maryland (omitting slavery) had far greater natural advantages for manufactures than Massachusetts. She had a more fertile soil, thus furnishing cheaper food to the working classes, a larger and more accessible coast, and nearly eight times the length of navigable rivers, greater hydraulic power, vast superiority in mines of coal and iron, a far more salubrious climate, cotton, the great staple of modern industry, much nearer to Maryland, her location far more central for trade with the whole Union, and Baltimore, her chief city, nearer than Boston to the great West, viz,: to the Ohio at Pittsburg and Cincinnati, the Mississippi at St. Louis, and the lakes at Cleveland, Toledo, and Chicago, by several hundred miles. Indeed, but for slavery, Maryland must have been a far greater manufacturing as well as commercial State than Massachusetts—and as to agriculture, there could be no comparison.

But Massachusetts did not become a manufacturing State until after the tariff of 1824. That measure, as well as the whole protective policy, Massachusetts earnestly opposed in 1820 and 1824, and Daniel Webster, as her representative, denounced it as unconstitutional. From 1790 to 1820 Massachusetts was commercial, not manufacturing, and yet, from 1790 to 1820, Massachusetts increased in numbers 144,442, and Maryland in the same time only 87,622. Yet, from 1790 to 1820, Massachusetts, the most commercial State, was far more injured by the embargo and the late war with England than any other State.

It is clear, then, that the accusation of the secession leaders that the North was built up at the expense of the South, by the tariff, can have no application to the progress of Massachusetts and Maryland, because the advance of the former over the latter preceded by more than thirty years the adoption of the protective policy, and a comparison of the relative advance of the free and slave States, during the same period, exhibits the same results.

There is one invariable law, whether we compare all the slave States with all the free States, small States with small, large with large, old with old, new with new, retarding the progress of the slaveholding States, ever operating, and differing in degree only.

The area of the nine free States enumerated in 1790, is 169,668 square miles, and of the eight slaveholding States 300,580 square miles, while the population of the former in 1790 was 1,968,455, and of the latter, 1,961,372; but, in 1860, these nine free States had a population of 10,594,168, and those eight slave States only 7,414,684, making the difference in favor of these free States in 1860 over those slave States, 3,179,844, instead of 7,083 in 1790, or a positive gain to those free States over those slave States of 3,172,761. These free States, enumerated in 1790 and 1860, were the six New England States—New York, New Jersey, and Pennsylvania; and the slave States were, Delaware, Maryland, Virginia, North and South Carolina, Georgia, Tennessee, and Kentucky—yet we have seen that the area of those slave States was nearly double that of those free States, the soil much more fertile, the climate more salubrious, as shown by the census, and the shore line, including main shore, bays, and sounds, islands and rivers, to head of tide water, was, for those free States, 4,480 miles, and for those slave States, 6,560 miles. Thus, it is clear, that the increase of population of these slave States should have far exceeded that of those free States. The population of these slave States per square mile in 1790 was six (6.52), and in 1860, 24 (24.66), and of those free States in 1790, was 11 per square mile (11.60), and in 1860, 62 per square mile (62.44). Thus, while the increase of those slave States from 1790 to 1860 was only 18 per square mile, that of those free States was nearly 51 per square mile (50.84), or in very nearly a triple ratio, while in wealth and education the proportionate progress was much greater.

No cause except slavery can he assigned for this wonderful difference, for the colonists of Maryland were distinguished for education, intelligence, and gentle culture. Lord Baltimore was a statesman and philanthropist, and his colony was a free representative government, which was the first to repudiate the doctrine of taxation without representation, and the first to introduce religious toleration. While Maryland has produced many of the most eminent soldiers, statesmen, and jurists, her relative decline in power, wealth, and population, has been deplorable, and is attributable exclusively to the paralyzing effect of slavery.

While the advance of Massachusetts, with her limited area and sterile soil, especially in view of the thousands of her native sons who have emigrated to other States, is one of the wonders of the world, yet, the relative increase of the population of New Jersey, from 1790 to 1860, compared with that of Maryland, is still greater than that of Massachusetts. The law is inflexible wherever slavery disappears. Population of New Jersey in 1790, 184,139, in 1860, 672,035, being an increase of 264 per cent. (264.96) for New Jersey, of 225 per cent. (225.06) for Massachusetts, and for Maryland 114 per cent. (114.88). The ratio of increase per square mile from 1790 to 1860 was: Massachusetts, 48.55 in 1790, and 157.82 in 1860; Maryland, 28.74 in 1790, and 61.76 in 1860; and New Jersey, 22.01 in 1790, and 80.70 in 1860. Thus, while Maryland from 1790 to 1860, little more than doubled her ratio of increase per square mile (28.74 to 61.76), and Massachusetts a little more than tripled her ratio (48.55 to 157.82), New Jersey very nearly quadrupled hers (22.01 to 80.70). It must be conceded, however, that the natural advantages of New Jersey are far greater than those of Massachusetts, whose material and intellectual progress, in defiance of such serious obstacles, now is, and, most probably forever will be, without a parallel. Now the area of New Jersey is but 8,320 square miles; the soil of Maryland is far more fertile, the hydraulic power much greater, the shore line much more than double, viz.: 531 for New Jersey, to 1,336 for Maryland; while New Jersey, with rich iron mines, has no coal, and one third of her area is south of the celebrated Mason and Dixon's line, the northern boundary of Maryland. The comparison, however, which I shall present hereafter, of New York and Virginia, will be the most astounding, while little less remarkable will be found that of North Carolina with Pennsylvania, Kentucky with Ohio, Tennessee with Indiana, Georgia and Missouri with Illinois, Arkansas with Michigan, Alabama and Texas with Iowa or Minnesota, Mississippi and Louisiana with Wisconsin, Delaware with Rhode Island, South Carolina with Maine or Vermont. All, however, prove the same law, and exhibit the same paralyzing effect of slavery. While the free States have accomplished these miracles of progress, they have peopled seven vast Territories (soon by subdivision to become many more States), immigration to which has been almost exclusively from the North, as compared with the South. It is clear, that if the South retains the institution, it will, before the close of this century, sink into comparative insignificance, and contain less than a sixth in population of the Union. After the calamities which slavery has brought upon the South, the ruin and desolation the rebellion has already accomplished there, who from the North or from Europe would hereafter immigrate to any State retaining the system?—while thousands of the native sons of the South have already fled North or to Europe, and hundreds of thousands will follow.

The slave State which has increased most rapidly to the square mile of all of them from 1790 to 1860, has had a smaller augmentation per square mile than that free State which has increased most slowly per square mile during the same time of all the free States, and the result is the same as to wealth and education also. Under the best circumstances for the slave States, and the worst