12.—Diagram of a modern spherical balloon with ripping panel 75 13.—Blanchard’s dirigible balloon, 1784 80 14.—Robert Brothers’ dirigible, 1784 82 15.—General Meusnier’s proposed dirigible, 1784 85 16.—Rufus Porter’s dirigible, 1820 87 17.—Jullien’s model dirigible, 1850 88 18.—Giffard’s steam dirigible, 1852 89 19.—Dupuy de Lome’s dirigible, 1872 92 20.—Renard’s dirigible, _La France_, 1884 94 21.—_La Ville de Paris_ 121 22.—_Le Petit Journal_, Zodiac type 128 23.—_Clément-Bayard II_, 1910 133 24.—_Morning Post_ dirigible, 1910 135 25.—Route of British military dirigibles from France to England, 1900 137 26.—Da Vinci’s helicopter 175 27.—Da Vinci’s parachute 176 28.—Veranzio’s parachute 178 29.—Lenormand’s parachute, 1784 179 30.—Paper traveling parachute 181 31.—Wenham’s aëroplane, 1866 185 32.—Penaud’s aëroplane toy, 1871 187 33.—Tatin’s aëroplane model, 1879 188 34.—Hargrave’s model screw monoplane, 1891 190 35.—Hargrave’s kite 191 36.—Launoy and Bienvenu’s helicopter, 1784 198 37.—Forlanini’s helicopter, 1878 200 38.—Le Bris’ aëroplane, 1855 204 39.—Mouillard’s aëroplane 208 40.—Blériot’s Toury-Artenay aëroplane circuit, 1908 269 41.—Map of the “Circuit de l’Est” 330 42.—Diagram of Curtiss hydro-aëroplane 333 43.—The Etrich monoplane of 1910 336 44.—Summer and winter average vertical temperature gradients 369 45.—General circulation of the atmosphere 378 46.—Normal Wind direction and velocity for January and February (Köppen) 381 47.—Normal Wind direction and velocity for July and August (Köppen) 383 48.—Trade and counter-trade winds 384