648 



NATURE 



{Oct. 17, 1878 



ON THE NATURE OF VIBRATORY MOTIONS^ 



III. 

 Experbnents by which Compound Sounds are analysed 



by viewing in a Rotating Mirror the Vibrations of 



Konig's Manometric Flames. 



TAKE a piece of pine board, A, Fig. 15, i inch 

 (25 millimetres) thick, \\ inch (38 millimetres) 

 wide, and 9 inches (22"8 centimetres) long. One inch 

 from its top bore with an inch centre-bit a shallow 

 hole \ inch deep. Bore a like shallow hole in the 

 block B, which is | inch thick, \\ inch wide, and 2 inches 

 (51 millimetres) long. 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 -j'^^-inch (5 millimetres) hole 

 obliquely into the shallow hole in B, and into this fit the 

 glass tube c. Then bore another j'^-inch hole directly 



Fig. is. 



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. 

 15. 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 ycu can 

 find, or a piece of thin linen paper, and, having rubbed 



J ^""""^ * forthcoming work on " Sound : a Series of Simple, Entertaining, 

 and Inexpensive Experiments in the Phencmena of Sound, f>.r the Use of 

 btudents of every Age." By Alfred Marshall Mayer, Professor of Physics 

 in the Stevens Institute of Technokgy. Communicated by the author. 

 (Continued from p. 5C6.) 



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 com- 

 partments 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 8 inches long and with a mouth 2 inches (51 milli- 

 metres) in diameter. 



Now get a piece of wood i foot long, 4 inches wide, 

 and \ 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 4 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 16. — 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 down- 

 ward 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 cone to your mouth and 

 sing into it. The sonorous vibrations enter thei 

 side A of the box, and, striking on the thin rubber, 

 force this in and out. When it goes in a puff of 

 gas is driven out of the other partition, B, of the box, 

 and the flame F jumps up. When the sheet of rub- 

 ber vibrates outward it sucks the gas into the box 

 B, and the flame F jumps down. Therefore, on 

 singing into the funnel, you will see in the mirror 

 the smooth top-border of the luminous band broken 

 up into little tongues or teeth of flame, each tooth 

 standing for one vibration of the voice on the rubber 

 partition. 



Place a lamp-chimney around the flame, should; 

 the wind from the twirling mirror agitate it, and' 

 be careful not to have the flame too high. 



Experiment 17. — Another way of showing the 

 vibrations of the flame is to burn the jet of gas at 

 the end of a glass tube stuck into the end of a rub- 

 ber tube attached to F. Now sling the tube round 

 in a vertical circle, and you have an unbrokerk 

 luminous ring; but as soon as you sing into the cone this 

 ring breaks up into a circle of beads of light, or sometimes 

 changes into a wreath of beautiful little luminous flowers, 

 like forget-me-nots. To make this experiment you will 

 be obliged to have a tube with a larger opening than that 

 at F. 



This instrument will afford you many an hour of in- 

 struction and amusement. We have only space to show 

 you a few experiments. Others will suggest themselves 

 whenever you use it. 



Expeiiment 18. — Sing into the funnel the sound of 

 00 as in -^ooX. After a few trials you will get a pure 

 simple sound, and the flame will appear as in Fig. 16. 

 Some voices get this figure more readily by singing E. 



Experiment 19. — Twirling the mirror with the same 

 velocity, gradually lower the pitch of the 00 sound till 

 your voice falls to its lower octave, when the flame will 



