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BELL SYSTEM TECHNICAL JOURNAL 



The type of vibration of the system in one of these patterns is called 

 "a normal mode." The patterns are described by two "quantum 

 numbers" p and g which are equal to one plus the number of nodal 

 lines (indicated by arrows) running across the membrane from front 

 to back and from right to left respectively. In Figs. 7b and 7c we 

 show the wave patterns corresponding to the Is and 25 states of the 

 atom; the quantum numbers of the V' waves are also correlated to 

 nodes. In the case of the membrane the frequencies and standing 



Fig. 7 — The atom and some mechanical and electrical analogues. 



(a) Potential energy of an electron in the atom. 



(b) The Is wave function. 



(c) The 2s wave function. 



(d) A mechanical analogue and 



(e) its normal mode of vibration. 



(f) An electrical analogue. 



(g) to (j) The first four normal modes of vibration of a stretched 



drum head. (From "Vibration and Sound" by P. M. 

 Morse, McGraw-Hill, New York, 1937. Courtesy of the 

 McGraw-Hill Book Co.) 



