side  of  the  disc  away  from  the  pipe  rising  very  suddenly  as
a  hole  comes  opposite  the  pipe  and  falling  very  suddenly
when  the  hole  has  passed,  instead  of  the  gradual  harmonic
rise  and  fall.  But  the  wave-form  of  these  waves,  as  Fourier's
theorem  shows,  might  be  made  by  adding  the  ordinates  of  the
wave-forms  of  harmonic  waves  11  feet,  -y-feet,  -^-feet,  &c.,
in  length.  So  that  harmonic  waves  of  these  lengths  are
harmonic  components  of  the  waves  from  the  disc,  although
to  produce  real  harmonic  waves  ±±  feet  long  would  require  a
movement  repeating  itself  exactly  300  times  in  each  second,
and  nothing  that  happens  at  the  source  is  repeated  with  this
frequency.
