Pianoforte Sounding-Board, 655 



for what purpose his opinion was asked, and it may therefore 

 be regarded as being without prejudice. 



In No. 8 the frequency of the strings was nearer to the 

 natural frequency of the sounding-board than in No. 7. The 

 length of strings and point struck were the same. 



It will be noticed that while the 2nd partial was not 

 apparent in No. 7 it was very strong in No. 8. This was not 

 expected, and it was suggested that the end of the straw, 

 where it was gripped by the nut on the optical lever, was 

 weak and in some way influenced the result. Accordingly 

 the nut was moved along the straw until it gripped as thick 

 a part of the tapered end of the straw as was possible. The 

 connexion was then quite stiff, but as will be seen from No. 9 

 the only effect was to reduce the amplitude of the vibration. 



In No. 10 the strings were of the same length and struck 

 at the same point. The pitch of the strings was nearly twice 

 that of the sounding-board. The amplitude of the 1st partial 

 was greater than in No. 7, and the tone of Nos. 7 and 10 was 

 much better than that of Nos. 8 and 9. It is clear that an 

 increased resonance is not to be obtained by making the 

 frequency of the sounding-board the same as that of the 

 strings. The bridge was in all these cases at or near the 

 middle of the sounding-board, and the only explanation seems 

 to be that the sounding-board divides in half with the bridge 

 as a node and when each half has a frequency near the pitch 

 of the strings a good note results. This is confirmed by the 

 marked resonance of the octave of the strings in Nos. 8 and 9. 

 In No. 11 we see that when the frequency of the sounding- 

 board is much below half that of the strings, a bad note is 

 also the result. The strings were 37 cm. long and 

 struck at -J. 



Nos. 12 and 13 were both described as being good. In 

 Nos. 14-16 the strings were 48 cm, long and struck at j-. 

 No. 15 gave ati excellent result, the tone was the best of the 

 series. The amplitude is very large, the wave regular and 

 free from pronounced upper partials. The pitch of the strings 

 was very nearly an octave above that of the sounding-board. 



In No. 16 the amplitude becomes rapidly smaller on the 

 print. This was due to the strings being slightly out of 

 unison. Beats were audible to the ear and also apparent on 

 watching the spot of light. If the exposure had been con- 

 tinued the amplitude would again have increased. 



Nos. 17-25 were all taken with longer sounding-board 

 sections and two copper-covered steel wires taken from the 

 corresponding note on a pianoforte. 



To get the distance between the bridges long enough to 



