70 Royal Institution : — 



have placed silvered beads at the nodes and at the centres of the 

 vibrating segments; you see the light shining from those beads, 

 and you notice that while the nodal beads remain stationary, the 

 others describe luminous lines. 



12. If I place sheets of paper across the wire at the nodes and at 

 the ventral segments, on causing it to vibrate thus, the sheets placed 

 across the ventral segments are tossed off, while those at the nodes 

 remain undisturbed. 



13. From these effects which you can actually see, I might pass 

 on to vibrating strings, and show you that they divide themselves, 

 similarly. I might also show you that it is hardly possible for a 

 musical string to vibrate as a whole without having these smaller 

 vibrations riding like parasites upon the large one. The addition 

 of these smaller vibrations gives quality or timbre, or, as the Germans 

 call it, Klangfarbe to the note. They constitute the harmonics of 

 the string. 



14. In this vice is fixed upright a rod of iron 4 feet long. I pull 

 it aside and it vibrates as a whole ; its vibrations are rendered more 

 distinct by casting its shadow upon a white screen. I now strike 

 the rod sharply at a point about one-third of its length from its 

 fixed end. The pulse runs along the rod, returns from its free 

 end, and is met by the succeeding pulses ; and now the rod is 

 divided into two vibrating parts — : a whole segment and a half seg- 

 ment, separated from each other by this dark motionless node. By 

 promptly striking the rod lower down, I cause it to divide into two 

 complete vibrating segments, forming those shadowy spindles upon 

 the screen, and half a segment at the top, which spreads out like a 

 fan. The nodes are marked by the two dark points where the 

 shadow is complete. 



15. This production of stationary undulations on a large scale 

 through the combination of direct and reflected waves, for the illus- 

 tration of which we are mainly indebted to the brothers Weber, 

 forms a fit introduction to the experiments of M. Melde of Mar- 

 burg, who has obtained a series of very beautiful effects by asso- 

 ciating with vibrating bodies suitably stretched strings. 



16. In M. Melde's first experiment he stretched a string across a 

 bell, or belljar, from edge to edge : when the bell was caused to 

 vibrate, the string vibrated also. By varying the tension of the 

 string it was caused to vibrate as a whole, or to divide itself intu 

 two, three, four, five, or more vibrating parts, separated from each 

 other by the appropriate number of nodes. 



17. He then attached his strings to tuning-forks, and obtained 

 the same effect in a more marked and beautiful manner. To this 

 tuning-fork I have attached a silk string which passes round a dis- 

 tant peg, by turning which the string is stretched. The length of 

 the string is 8 feet. The tension of the present moment is such 

 that when the fork is caused to vibrate, the string swings as a whole, 

 its periods of vibration being synchronous with the impulses im- 

 parted to it by the fork. We have here a beautiful gauzy spindle 

 produced by the silk, fully 6 inches wide at its point of greatest 

 amplitude. 



