[JJ] Mulhall’s estimate, except 1830, 1890, 1900, 1906, and 1907.

[KK] Steam tonnage reduced to sail by multiplying by 4.

[LL] Soetbeer’s estimates prior to 1860.

[MM] Malte-Brun’s estimate for 1804.

[NN] Based on Balbi’s estimate for 1828.

[OO] Based on Michelet’s estimate for 1845.

[PP] Based on Behm-Wagner estimate for 1874.

[QQ] Levasseur’s estimate for 1878.

[RR] Royal Geographic Society estimate.

[SS] Estimates of the Archiv für Eisenbahnwesen.