188 



LETTERS ON NATURAL MAGIC. 



rosined fiddle-bow drawn across the rod, it will 

 divide itself into two vibrating portions AB, BC, 

 each of which will vibrate, as . shown in Fig. 42, 

 like the two adjacent columns of air, the section 

 of the rod, or the particles which compose that 

 section at B, being at perfect rest. By holding 

 the rod at any intermediate point between A and 

 B, so that the distance from A to the finger and 

 thumb is one-third, one-fourth, one-fifth, &c. of 

 the whole length AC, and rubbing one of the 

 divisions in the middle, the rod will divide itself 

 into 3, 4, 5, &c. vibrating portions, and give out 

 corresponding harmonic sounds. 



A rod of iron may be made to vibrate laterally 

 or transversely, by fixing one end of it firmly, 

 as in a vice, and leaving the other free, or by 

 having both ends free or both fixed. When a 

 rod, fixed at one end and free at the other, is 

 made to vibrate, its mode of vibrating may be 

 rendered evident to the eye ; and for the purpose 

 of doing this, Mr. Wheatstone has contrived a 

 Fig. 43. 



