and air on the outside, so that the case of flame is between the air
and the gas. The gas keeps going into the flame to burn, and when the
candle burns properly, none of it ever passes out through the flame;
and none of the air ever gets in through the flame to the gas. The
greatest heat of the candle is in this skin, or peel, or case of
flame."

"Case of flame!" repeated Mr. Bagges. "Live and learn. I should have
thought a candle-flame was as thick as my poor old noddle."

"I can show you the contrary," said Harry. "I take this piece of white
paper, look, and hold it a second or two down upon the candle-flame,
keeping the flame very steady. Now I'll rub off the black of the
smoke, and--there--you find that the paper is scorched in the shape
of a ring; but inside the ring it is only dirtied, and not singed at
all."

"Seeing is believing," remarked the uncle.

"But," proceeded Harry, "there is more in the candle-flame than the
gas that comes out of the candle. You know a candle won't burn without
air. There must be always air around the gas, and touching it like, to
make it burn. If a candle hasn't got enough air, it goes out, or burns
badly, so that some of the vapor inside of the flame comes out through
it in the form of smoke, and this is the reason of a candle smoking.
So now you know why a great clumsy dip smokes more than a neat wax
candle; it is because the thick wick of the dip makes too much fuel in
proportion to the air that can get to it."

"Dear me! Well, I suppose there is a reason for everything," exclaimed