974 Messrs. Morton and Vinycomb on Vibrations of 
by another string, tuned to the same pitch and mounted on 
the same supporting frame. We wished tosee how promptly 
and how closely the primary vibrations were copied by the 
secondary string. The primary string was plucked, as this 
gives a characteristic and definite form of vibration-curve. 
At an early stage in the experiments we noticed certain 
peculiarities in the vibration-forms of the plucked string 
which called for explanation. In the experiments of Krigar- 
Menzel and Raps these forms gradually diverged from the ideal 
in a certain definite way, which they showed could be explained 
by the yielding of the supports at the ends of the string. In 
some of our photographs quite different forms appeared. We 
made further experiments in order to find out the cause of 
these differences ; and in the course of them we examined 
the effect of altering the size, tension, and material of the 
string, and also the nature of the supporting structure. 
Experimental Arrangement. 
In our arrangement the string, placed horizontally, was 
drawn aside in the vertical plane and held in a notch cut in 
the edge of a vertical blade, near its lower end. The blade 
was movable on a horizontal axis, parallel to the string, and 
carried at its upper end a piece of soft iron which could be 
drawn aside by an electromagnet, so releasing the string 
Parallel and close to the notched blade was a fixed blade. 
Its edge, bearing against the string, prevented it from following 
the notch when the latter was drawn aside. The efficient 
action of this “ plucker’’ was shown by the conformity of the 
first vibrations of the string to the theoretical form. The 
whole arrangement was made to work electrically. The photo- 
graphic plate was carried by a long pendulum. This was 
held back by an electromagnetic catch, and released by 
depressingakey. Ata certain point of its course the pendulum 
knocked over a key actuating the “ plucker,”’ and when at 
the middle of its swing it came in the path of the beam of 
light from the lantern. By varying the position of the 
plucking-key we could get different stages of the motion 
caught on the plate. 
Theoretical Motion of Ideal String with Fixed Ends. 
The theoretical motion of a plucked string may be described 
as follows*. Initially the string is made up of two straight 
pieces meeting at the point of discontinuity where the string 
* Helmholtz, ‘Sensations of Tone’ (Eng. trans.), p. 54; Rayleigh, 
‘Sound,’ vol. i. p. 231]. 
