ACOUSTICAL DISCOVERIES. 67 



THE LATE SIR CHARLES WHEATSTONE'S ACOUSTICAL 

 DISCOVERIES. 



Professor W. G. ADAMS, M.A., F.R.S.: If I were to speak of all the 

 instruments or even of all the musical instruments which may be 

 connected in some way or other with the name of Sir Charles Wheat- 

 stone, I am afraid I should occupy a very considerable time, weary 

 you, and shut out those who have to come after me; but I propose 

 to draw your attention to three classes of instruments with which Sir 

 Charles Wheatstone was specially connected. First of all, if we con- 

 sider the vibration of reeds, we may start from the very ancient 

 instrument the Marimba, which has iron rods fixed into a sounding 

 body in the same way as the iron fiddle, which consists of rods fixed at 

 one end to a sounding board, from the iron fiddle, by lengthen- 

 ing the rods, we get to the kalcidophone, which is so well known, 

 and the figures traced out by which are so familiar, that it will 

 not be necessary for me to describe them in detail. If we take 

 a cylindrical rod with one end fixed, and cause it to vibrate, being 

 cylindrical, it will vibrate transversely at tiie same rate in all direc- 

 tions, but it may be put in vibration so as to give not only a simple 

 figure, the ellipse, circle, or straight line, but by dividing it by nodes 

 or points of rest into separate vibrating segments we may get also the 

 super-position of the partial vibration figures combined with the 

 original simple figures. 



The simple figures are obtained by causing the rod to vibrate as a 

 whole, and the partial vibrations are obtained by producing one or 

 more nodes on the rod. The ratio of the number of partial vibrations 

 to the number of fundamental vibrations is given by the number of 

 indentations produced in the original figure traced out by the free 

 end of the rod. The number of vibrations when there is one node 

 on the rod is about 6- times the original number of vibrations of the 

 rod when it vibrates as a whole. With one, two, three or more nodes 

 the number of vibrations is as the squares of the second, third, or 

 higher odd numbers. No. of nodes, I, 2, 3, 4, &c. ; No. of vibrations, 9, 

 25, 49, 8 1, &c. With a rectangular rod. when its section is a square, 

 the curves traced out are the circle, the ellipse, or the straight line, 



