266 EIGHTEENTH CENTURY. PT. in. 



the centre almost still, and the two divisions each vibrate 

 twice as fast as the whole string did. 



This is very simple ; but now place the feather so as to 

 divide off one-third of the string, leaving two-thirds at the 

 other end ; it would seem as if you ought to have two 

 notes, one for the short string and one for the long one. 

 But you will only get one note, and that will be one-fifth 

 above the octave you had sounded just before. That is to 

 say, you will get the same note as you would have had if the 

 string ended at the feather and the other long piece did 

 not sound at all. Yet you can -easily convince yourself 

 that the whole string is vibrating, and what is still more 

 curious, that it has divided itself into three short strings, 

 each one of which is vibrating as if it were quite separate 



FIG. 4 8. 



A stretched string damped at one-third of its length, c, and dividing with a natural 

 node, or point of rest, between the remaining two-thirds at b (Tyndall). 



To see this, take three small pieces of light paper bent so 

 that they will ride upon the string. Then measure off your 

 string into three equal parts and touch one of the dividing 

 points (^, Fig. 48), with the feather ; place one of the paper 

 riders upon the other dividing point b, and the other two, 

 one half-way between a and l>, the other between b and c\ 

 If you now draw the bow across the string between c and d. 



