November, 1795. One day after dinner, the candles had been left for some time without being snuffed; and Mr. —— said he wished candles could be made which would not require snuffing.
Mrs. ******** thought of cutting the wick into several pieces before it was put into the candle, that so, when it burned down to the divisions, the wick might fall off. M—— thought that the wick might be tied tight round at intervals, before it was put into the candle; that when it burned down to the places where it was tied, it would snap off: but Mr. —— objected, that the candle would most likely go out when it had burned down to her knots. It was then proposed to send a stream of oxygene through the candle, instead of a wick. M—— asked if some substance might not be used for wicks which should burn into powder, and fly off or sublime. Mr. —— smiled at this, and said, "Some substance; some kind of air; some chemical mixture! A person ignorant of chemistry always talks of, as an ignorant person in mechanics always says, "Oh, you can do it somehow with a spring."
As the company could not immediately discover any way of making candles which should not require to be snuffed, they proceeded to invent ways of putting out a candle at a certain time without hands. The younger part of the company had hopes of solving this problem, and every eye was attentively fixed upon the candle.
"How would you put it out, S——?" said Mr. ——. S—— said, that if a weight, a very little lighter than the extinguisher, were tied to a string, and if the string were put over a pulley, and if the extinguisher were tied to the other end of the string, and the candle put exactly under the extinguisher; the extinguisher would move very, very gently down, and at last put out the candle.
Mr. —— observed, that whilst it was putting out the candle, there would be a disagreeable smell, because the extinguisher would be a considerable time moving very, very gently down, over the candle after the candle had begun to go out.
C—— (a girl of twelve years old) spoke next. "I would tie an extinguisher to one end of a thread. I would put this string through a pulley fastened to the ceiling; the other end of this string should be fastened to the middle of another thread, which should be strained between two posts set upright on each side of the candle, so as that the latter string might lean against the candle at any distance you want below the flame. When the candle burns down to this string, it will burn it in two, and the extinguisher will drop upon the candle."
This is the exact description of the weaver's alarm, mentioned in the Philosophical Transactions which C—— had never seen or heard of.
Mr. —— now showed us the patent extinguisher, which was much approved of by all the rival inventors.
It is very useful to give children problems which have already been solved, because they can immediately compare their own imperfect ideas with successful inventions, which have actually been brought into real use. We know beforehand what ideas are necessary to complete the invention, and whether the pupil has all the necessary knowledge. Though by the courtesy of poetry, a creative power is ascribed to inventive genius, yet we must be convinced that no genius can invent without materials. Nothing can come of nothing. Invention is nothing more than the new combination of materials. We must judge in general of the ease or difficulty of any invention, either by the number of ideas necessary to be combined, or by the dissimilarity or analogy of those ideas. In giving any problem to children, we should not only consider whether they know all that is necessary upon the subject, but also, whether that knowledge is sufficiently familiar to their minds, whether circumstances are likely to recall it, and whether they have a perfectly Clear idea of the thing to be done. By considering all these particulars, we may pretty nearly proportion our questions to the capacity of the pupil; and we may lead his mind on step by step from obvious to intricate inventions.