EXPERIMENTS IN SOUND. 73 



Place a -^^-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 ^inch (5 millimetres) hole obliquely 

 into the shallow hole in J?, and into this fit the glass tube C. Then 

 bore another j^^-inch hole directly into the shallow hole in £. 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 Z>, Fig. 51. Now fit this tube into the hole just made, as 

 shown at D. These tubes may be firmly and tightly fitted by wrap- 

 ping 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 ^ to ^ 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 F^ 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 3f. 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 .2" for the rod and square to twirl in. Glue the 

 piece of wood IC 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 iead 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 E, 

 and hold the mirror upright, so that you may see the flame F re- 

 flected 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 



