Place a 12-inch centre-bit in the centre of the shallow hole in A and bore with it a hole through the wood. Into this fit a glass or metal tube, as shown at E. Bore a 316-inch (5 millimetres) hole obliquely into the shallow hole in B, and into this fit the glass tube C. Then bore another 316-inch hole directly into the shallow hole in B. Put a glass tube in a gas or spirit flame and heat it red-hot at a place about two inches from its end. Then draw the tube out at this place into a narrow neck. Make a cut with the edge of a file across this narrow neck, and the tube will readily snap asunder at this mark. Then heat a place on the tube in a flame, and here bend it into a right angle, as shown at D, Fig. 51. Now fit this tube into the hole just made, as shown at D. These tubes may be firmly and tightly fitted by wrapping their ends with paper coated with glue before they are forced into their holes.
Get a small piece of the thinnest sheet rubber you can find, or a piece of thin linen paper, and, having rubbed glue on the board A around the shallow hole, stretch the thin rubber, or paper, over this hole and glue it there. Then rub glue on the block B, and place the shallow hole in this block directly over the shallow hole in A, and fasten B to A by wrapping twine around these blocks. Thus you will have made a little box divided into two compartments by a partition of thin rubber. Fasten the rod A to the side of a small board, so that it may stand upright.
Attach a piece of large-sized rubber tube to the glass tube E, and into the other end of the tube stick a cone, made by rolling up a piece of cardboard so as to form a cone eight inches long and with a mouth two inches (51 millimetres) in diameter.
Now get a piece of wood one foot long, four inches wide, and a quarter of an inch thick. Out of this cut the square, with the two rods projecting from it, as shown at M. The lower of these rods is short, the one above the square is long. Cut the end of the shorter rod to a blunt point, and with this point make a very shallow pit in the piece of flat wood K for the rod and square to twirl in. Glue the piece of wood K on the end of a brick, L. Get two pieces of thin silvered glass, each four inches square, and, placing one on each side of the square M, fasten them there by winding twine around the top and bottom borders of the mirrors.
Experiment 112.—Through a rubber tube lead gas to C. It will go into the left-hand partition of the box and will come out at F, where you will light it. Now place the mirror-rod in the shallow pit in K, and hold the mirror upright, so that you may see the flame F reflected from its centre.
Hold the rod upright and twirl it slowly between the thumb and forefinger, which should point downward and not horizontally, as shown in the figure. The flame appears in the mirror drawn out into a band of light with a smooth top-border. While twirling the mirror put the
