In the 1700's, there were no cameras. One's image was either sculpted or painted. Some paintings of George Washington showed him standing behind a desk with one arm behind his back while others showed both legs and both arms. Prices charged by painters were not based on how many people were to be painted, but by how many limbs were to be painted. Arms and legs are "limbs," therefore painting them would cost the buyer more. Hence the expression. 
"Okay, but it'll cost you an arm and a leg."
As incredible as it sounds, men and women took baths only twice a year! (May and October) Women kept their hair covered, while men shaved their heads (because of lice and bugs) and wore wigs. Wealthy men could afford good wigs made from wool. The wigs couldn't be washed, so to clean them they could carve out a loaf of bread, put the wig in the shell, and bake it for 30 minutes. The heat would make the wig big and fluffy, hence the term "big wig." Today we often use the term "here comes the Big Wig" because someone appears to be or is powerful and wealthy.
Marquis d'Arlandes
Pilatre de Rozier
1783 --- 1st humans to fly. They were airborne in a hot-air balloon for 20 minutes, in Paris, on Nov. 21.

André-Jacques Garnerin 
1797 --- 1st parachute jump. Dropped from a balloon, about 6,500 ft. over Monceau Park in Paris in a 23-ft.-diameter parachute made of white canvas with a basket attached (Oct. 22).
Count de Grisley
1799 --- 1st magician to perform the trick of sawing a woman in half .