156 Vibration Curves from Monocliord. 



amplitudes are equal and their phase-difference about |. 

 Hence the actual frequency o£ the higher component to 

 which the belly responded so well was about 306 per second. 

 This led us to believe that the sound-box had a special 

 resonance at or near this pitch. To test this the next experi- 

 ment was made. 



Figure 12 shows the result o£ exciting the vibrations of the 

 belly, not by the string, but by a trombone with its bell near 

 the middle of the sound-box. The note sounded was e'\), of 

 frequency about 320 per second. Before exposing the plate, 

 this pitch was chosen as the most effective by watching the 

 motion of the spot of light. It moved a little for d' (say 

 306 per second), but much better for e'\). The string was of 

 course unmoved by the powerful blast which awakened such 

 marked resonance in the belly. The belly's motion is also 

 seen to be practically a pure sine graph. 



Figure 13 shows the same vibrations elicited from the belly 

 as in figure 12, but this time by means of the string. This 

 note could not be obtained direct as the fundamental tone of 

 the string, since the bridges would not bear the pressure due 

 to the necessary tension. Neither did it seem advisable to 

 produce the note as the second partial tone of the string, as 

 this would have a node in the middle near our place of 

 observation. The string was accordingly tuned down to a 

 frequency of about 107 per second, and the required note 

 (320 per second) produced as the third partial tone. The 

 string was lightly touched at 33J cm., bowed at 7 cm., and 

 observed at 44*5 cm. The leg of the optical lever was on the 

 glass-headed pin at 50*5 cm. The photograph shows a very 

 small motion of the string which is almost simple harmonic. 

 The belly's motion is relatively large, and strictly simple 

 harmonic as in the previous plate. Thus figures 11, 12, and 

 13 all agree in establishing a distinct resonance of the belly 

 for a frequency of the order 320 per second. 



Figures 14 to 26 y occupying the second column of the 

 Plate, illustrate the series of effects obtained by tuning the 

 string to the successive notes of the equally-tempered 

 chromatic scale through an octave. Throughout this set, the 

 string was bowed at 90 cm. and observed at 44' 8 cm. The 

 leg of the optical lever was at 50 cm. and rested on glass 

 cemented direct on the belly. The thirteen photographs were 

 taken in one day, the negatives being stored in numbered 

 light-tight bags for subsequent development. The frequencies 

 ranged from 92 to 184 per second, and are shown in the space 

 between the second and third columns of figures. These 

 pitches were chosen so that the third partial of the lowest 



