450 Prof. Barton and Mr. Penzer on Simultaneous 



motion is inverted. The bridge's motion vertically in figs. 

 1-6 and 14-26 is also shown inverted. In figs. 7-13 and 

 27-47 showing the motion of the bridge horizontally the 

 high positions of the spot denote a yielding of the bridge 

 towards the centre of the string. 



Results. — The curves obtained by these experiments are 

 represented in the 47 photographs on Plates XL and XII., each 

 showing the simultaneous vibrations of string and bridge. 

 These fall naturally into five groups which are taken in order 

 below. 



Group I. includes figs. 1-6 in column 1 of Plate XI. 

 These show the vertical movements of the bridge, the string- 

 being excited by bowing and plucking at the places shown 

 in the margin of the plate. 



Group II. includes figs. 7-13 in column 1 of Plate XL 

 These show horizontal motions of the bridge parallel to the 

 length of the string, the string being excited by bowing and 

 plucking as noted against each figure. Two examples of 

 beats are represented in figs. 9 and 10. In the former the 

 string had a frequency of 138 per second and was plucked at 

 10 cm. from the bridge whose motion is shown, while a fork 

 of 128 per second was excited by striking and then held ver- 

 tically with its stem on the belly of the sound-box at 18 cm. 

 from the bridge. The photographic plate was also shot 

 slower than usual in the hope of showing a couple of maxima 

 or minima of the resultant vibrations. This state of things 

 was not obtained, but as the left end of the print indicates 

 the beginning of the time we see there is evidence of in- 

 creasing amplitude, thus proving that the bridge could take 

 up vibrations from a fork on the belly although the string- 

 was passing over it and vibrating at a different frequency. 

 This plate paved the way for the next, fig. 10, in which beats 

 were obtained by the device of making them 18 per second 

 instead of 10 and shooting the plate still slower than before. 

 In this case the frequency of the string was raised to 146 

 per second, and the 128 fork was held upright with its stem 

 on the bridge near the point B in fig. 2. The string as 

 before was plucked at 10 cm. from this bridge. The upper 

 half of the print shows clearly two maxima of the resultant 

 vibrations of the bridge, while the lower part shows that the 

 string's vibrations were dying away. 



Group III. consists of figs. 14-26 contained in column 2 

 of Plate XL Here bowing at a tenth of the string's length 

 is adhered to throughout, the pitches forming the tempered 

 chromatic scale of frequencies 92 to 184 per second. All the 

 figures in this group show the vertical motions of the bridge. 



