Oct. 3, 1878] 



NATURE 



595 



fourth columns the corresponding lengths of the longer 

 and shorter pendulums. Opposite these lengths are 

 the figures which these double pendulums trace. In the 

 sixth column are the names of the musical intervals 

 formed by two notes, which are made by numbers of 

 sonorous vibrations, bearing to each other the ratios given 

 in the first and second columns. 



Mm. 

 2 = 1,000 



Mm. 

 250-0. 



2:3= 1,000 : 444-4. 



3:4= 1,000 : 562-5. 



4:5 = 1,000 : 640"o. 



5:6= 1,000 : 694-4. 



6 : 7 rz: 1,000 : 734-6. 



7:8= 1,000 : 766'6. 



■8 : 93= 1,000^: 790-1. 



Octave. 



Fifth. 



Fourth. 



Major Third. 



Minor Third. 



Sub-Miiior TliJrd. 



Super Second. 



Second. 



Fig. 10. 



Prof. Kundi's Experiment, made with a Whistle and a 

 Lamp Chimtiey, showing that, as in Wind Instru- 

 ments, a vibrating Column of Air may originate 

 Sonorous Vibrations. 



Experiment 10. — The chimneys of student-lamps have 

 a fashion of breaking just at the thin, narrow part near 

 the bottom. Such a broken chimney is very useful in 

 our experiments. At A, in Fig. 11, is such a broken 

 chimney, closed at the broken end with wax. A cork is 

 fitted to the other end of the chimney, and has a hole 

 bored through its centre. In this hole is inserted part of 

 a common wooden whistle. At B is an exact representa- 

 tion of such a whistle, and the cross-line at c shows 

 where it is to be cut in two. Only the upper part is used, 

 and this is tightly fitted into the cork. 



Inside the tube is a small quantity of very fine pre- 

 cipitated silica, probably the lightest powder known. 

 Hold the tube in a horizontal position and blow the 

 whistle. The sihca powder springs up into groups of 

 ihin vertical plates, separated by spots of powder at rest, 



as in the figure. This is a very beautiful and striding 

 experiment. 



Experiment 11. — The following experiment shows 

 that the sound is caused by the vibrations of the column 

 of air in the tube and whistle, and not by the vibrations 

 of these soHd bodies. Grasp the tube and whistle tightly 

 in the hands. These bodies are thus prevented from 

 vibrating, yet the sound remains the same. 



The breath driven through the mouth of the whistle 

 strikes on the sharp edge of the opening at the side of 

 the whistle, and sets up a flutter or vibration of air. The 

 air within the glass tube now takes part in the vibrations, 

 the light silica powder vibrates with it, and makes the 

 vibrations visible. 



To exhibit this experiment before a number of people, 

 lay the tube carefully on the water-lantern before the 

 heliostat, and throw a projection of the tube and the 

 powder on the screen. When the whistle is sounded, all 

 in the room can see the fine powder leaping up in the 

 tube into thin, upright plates. 



Experimefit 12. — Mr. Geyer has made the foUo.ving 



Fig. II. 



pleasing modification of this experiment : — Take a glass 

 tube about 2 feet (61 centimetres) long and J inch (19 

 millimetres) diameter. One end of this tube is stopped 

 with a cork ; then some silica is poured into it. The other 

 end is placed in the mouth. Singing into the tube, a note 

 is soon struck which causes the silica to raise itself in 

 groups of vertical plates, separated by places where the 

 powder is at rest, the number of these groups and their 

 positions in the tube changing with the note sung. 



We have now seen how solids, like steel or brass, may 

 vibrate and give a sound. We have heard a musical 

 sound from vibrating water, and these last experiments 

 prove that a gas, like air, may also vibrate and give a 

 sound. In the next chapter you will find experiments 

 which show how these vibrations move through solids, 

 through liquids, and through the air. 



On the Interference of Sonorous Vibrations and oti the 

 Beats of Sound. 



Experinunt 13. — Cut out. two small triangles of copper 

 foil or tinsel, of the same size, and with wax fasten one 

 on the end of each of the prongs of a tuning-fork. Put 

 the fork in the wooden block and set up the guide. 

 Prepare a strip of smoked glass, and then make the fork 

 vibrate and slide the glass under it, and get two traces, 

 one from each prong. 



Holding the glass up to the light you will see the 

 double trace, as shown in Fig. 12. You observe that the 



Fig. 12. 



wavy lines move apart and then draw together. This 

 shows us that the two prongs, in vibrating, do not move 

 in the same direction at the same time, but always in 

 opposite directions. They swing toward each other, then 

 away from each other. 



Experiment 14. — What is the effect of this movement 



