To His Excellency Benjamin Franklin December, 31 1785
TO HIS EXCELLENCY BENJAMIN FRANKLIN, ESQUIRE December 31, 1785.
I send you the candles I have been making. In a little time after they are lighted the smoke and flame separate, the one issuing from one end of the candle, and the other from the other end. I suppose this to be because a quantity of air enters into the candle between the tallow and the flame, and in its passage downwards takes the smoke with it; for if you blow a quantity of air up the candle, the current will be changed, and the smoke reascends, and in passing this the flame makes a small flash and a little noise.
But to express the idea I mean, of the smoke descending more clearly it is this,-that the air enters the candle in the very place where the mellow tallow is getting into the state of flame, and takes it down before the change is completed-for there appears to me to be two kinds of smoke, humid matter which never can be flame, and inflammable matter which would be flame if some accident did not prevent the change being completed-and this I suppose to be the case with the descending smoke of the candle.
As you can compare the candle with the lamp, you will have an opportunity of ascertaining the cause-why it will do in the one and not in the other. When the edge of the enflamed part of the wick is close with the edge of the tin of the lamp no counter current of air can enter-but as this contact does not take place in the candle a counter current enters and prevents the effect in the candles which illuminates the lamp. For the passing of the air through the lamp does not, I imagine, burn the smoke, but burns up all the oil into flame, or by its rapidity prevents any part of the oil flying off in the state of half-flame which is smoke.
I do not, my dear sir, offer these reasons to you but to myself, for I have often observed that by lending words for my thoughts I understand my thoughts the better. Thoughts are a kind of mental smoke, which require words to illuminate them.
I am affectionately your obedient and humble servant,
I hope to be well enough tomorrow to wait on you.