SOUND 267 



best and illuminating the whole by the lantern beam sent 

 along the string at a small angle. For a multitude of figures 

 a very thin and narrow ribbon rather closely twisted will be 

 best ; for fewer and more distinct figures, a broader one with 

 only a few twists. A large fork is almost indispensable for 

 such experiments, but may be quite a rough one, as before 

 described. An electrical fork is of course much the best and 

 most convenient, and may be obtained for about 51. 



Very good figures may however be also displayed by 

 employing the covered string of a violoncello, on which 

 silvered beads are strung, mounted on a sonometer and 

 vibrated with a bow. (Covered strings give much larger 

 figures, not being so tightly strained.) Any single bead can 

 be projected ; and I have found it quite possible to project in 

 this way the figure described by the G string of a violin ; but 

 the effect is hardly worth the time taken in arranging the 

 experiment. 



145. Harmonics, and Melde's Experiments. These ex- 

 periments are certainly best shown direct, on a large scale, 

 with an electrical fork, and using strings either steeped in 

 fluorescent solution, in violet light from the lantern, or what 

 is still better, painted with Balmain's phosphorescent paint. 

 Or the shadow method may be employed, when the arcs and 

 nodes will be enlarged. But it may be useful to know that 

 they can be demonstrated by projection with quite small and 

 inexpensive apparatus, using a common c fork of 256 vibra- 

 tions, or the G above it, and a cord of fine sewing-silk only 6 

 inches long from point to point, exciting the fork with a 

 bow. I have found the best practical limits of weight to be 

 between 10 and 80 grains for this small scale. A much more 

 convenient apparatus could easily be constructed in which, 

 instead of using weights, the other end of the silk should be 

 attached to a helical spring, the tension of which could be 

 varied as required by a lever. Quite a small fork say c 256 

 could even be fitted in this way to act electrically, bringing 



