All these explanations and speculations are fine and dandy, except ... How were the fires lighted 200-300 years ago?!? Who knew then about glycerine, kerosene and other technology that was invented in the past century? Try to think back in time and how you would do it with the then-technology and materials. Kind of ... how were the pyramids built? Please publish the answer when you think you know it ... I am too lazy to think right now.