From the middle the frame will spread of course to the two extremities and light the other two matches, probably this side first where the two phosphorous heads meet.
Well, nothing of the sort happens. When the volume of the burning match has diminished, and consequently its rigidity also, the force of its resistance grows weaker as the combustion proceeds.
A moment comes when the two vertical matches, trying to assume again their original position, throw off, with a sway, the burning horizontal match.
The burning match was rendered flexible in the middle, and is not at all burned at the ends, and the two matches remain standing as before.
To Make an Exact Balance.
To construct by yourselves, with the help of simple materials a balance of great precision may seem impossible. Nevertheless it can be done.
A ruler, a tin box, (in which blacking was contained, for example) three blocks of wood, two pins, thread, four nails, a small piece of glass, and cardboard are all the necessary materials, and now to work.
At a short distance from the center of the ruler, and on a cross line with one another, stick two pins so that they come out a little on the other side. At one end of the ruler, in C, nail a small piece of your box.