THE CANDLE FLAME
You will see a candle is a very different thing from a lamp. With a lamp you take a little oil in a vessel, insert a wick, then light the top of the wick. When the flame runs down the wick to the oil, it gets extinguished, but it goes on burning in the part above.
Now, I have no doubt you will ask, how is it that the oil which will not burn itself, gets up to the top of the wick, where it will burn? We shall presently examine that; but there is a much more wonderful thing about the burning of a candle than this.
You have here a solid substance with no vessel to contain it; and how it is that this solid substance can get up to the place where the flame is? How is it that this solid gets there, it not being fluid? or, when it is made fluid, then how is it that it keeps together?. This is a wonderful thing about a candle.
Notice a candle which has been burning a little while. Observe that a beautiful cup is formed just under the flame. As the air comes to the candle it moves upward by force of the current which the heat of the candle produces, and it so cools all the sides of the wax as to keep the edge cooler than the part within; the part within melts by the flame that runs down the wick, but the part outside does not melt.
If I made a current in one direction, my cup would be lop-sided, and fluid would consequently run over. For the same force of gravity, which holds worlds together holds the fluid in a horizontal position, and if the cup be not horizontal, of course the fluid will run away in guttering.
(from Michael Faraday's 'Lectures on the Chemical History of a Candle' given to an audience of the young several times up to 1860. In them he coaxed the candle to give up its secrets, cunningly using it to demonstrate many physical and chemical laws; always illustrated practically with candles and other equipment before him in the lecture theatre of the Royal Institution, London. From simple beginnings as above, he progresses to water, carbon, gases, respiration, showing how scientists investigate and discover.
His occasional suggestion that "This is a good experiment for you to make at home" must have scared the parents present!)