[Footnote 180: Other things which perhaps ought to be considered, but which do not seem to modify results are mentioned in this note; i.e., the mortality on the sugar plantations (Stearns' Notes on Uncle Tom's Cabin, pp. 174-5), and the deaths caused by removal of slaves from a northern climate (Olmsted: Journey in the Back Country, 122; Chambers: Slavery and Color, 147-8). Negroes advertised for sale in the far South were often advertised as acclimated (Mississippi Republican, Sept. 17, 1823; Daily Picayune, Jan. 30, 1856). To offset the loss of life thus caused it is well to remember that the increase of slaves carried to the South was not taken into account, but treated as if they too were carried there. For instance, 1,000 slaves imported in 1830 would at a 20 per cent. rate of increase number 1,200 by 1840, or to take the middle date 1835, 1,100. So each 1,000 slaves brought in during the decade would increase by 100. If 40,000 were introduced by the illicit foreign traffic between 1830 and 1840, and 106,000 by the trade from the border States, it would mean a natural increase of 14,600 for the ten years. This it seems would offset both the deaths on the sugar plantation, and those caused by removal to another climate. Next to be considered are refugees and manumitted slaves; Miss Martineau said that there were about 10,000 negroes in Upper Canada about 1838, chiefly fugitive slaves (W. Travel., Vol. II., p. 101). The Census of 1860 reports that (Vol. Pop. XVI.) 1,011 slaves escaped in 1850, and only 803 in 1860, and that the slave population increased in slave states more than 20 per cent. during the 10 years, and free colored population in the free States only about 13 per cent. It is estimated in De Bow's Industrial Resources (Vol. III., p. 129) that about 1,540 annually escaped. (For other estimates see Seibert Underground R.R., pp. 192, 221 et seq.) The Census of 1860 reports that more than 3,000 were manumitted in census year of 1860, but this was more than twice as many as in 1850. (1860 Vol. Pop., p. XV.). To offset the fugitive slaves and those manumitted the following is given: kidnapped free negroes from a few hundred to two or three thousand yearly free negroes sold into slavery for jail fees, etc. Liberator, Nov. 19, 1841, July 17, 1834; Speech of Mr. Miner in Congress Jan. 7, 1829; (Sturge: A Visit to the U.S., p. 101) voluntary return to slavery--many States made laws before 1860 to provide for such action on the part of the slaves. (Hurd, Vol. II., p. 12, 24, 94, et seq.).