program AINDEX 
C
C   Calculates the index of refraction (n-1) of air for pressure P (mb)
C   temperature T (kelvins) partial pressure of water E (mb) and
C   wavelength WAVE (microns).
C
      IMPLICIT UNDEFINED (A-Z)
      REAL *8 P, T, E, INDEX1,index2, A, B, K, WAVE1,wave2,wave
      real*8 dispers
C
   10 write(6,*)'Enter P, T, E, Wavelength 1,2'
      read(5,*)p,t,e,wave1,wave2
      wave=wave1
      K = 1./(WAVE*WAVE)
      A = 1.E-8*( 2372.434 + 684255.24/(130.-K) + 4549.40/(38.9-K) )
      B = A - 1.E-8*(6487.31 +K*( 58.058 +K*(-0.71150 +K*0.08851 ) ) )
      INDEX1 = ( A*P - B*E ) / T +1.D0
      wave=wave2
      K = 1./(WAVE*WAVE)
      A = 1.E-8*( 2372.434 + 684255.24/(130.-K) + 4549.40/(38.9-K) )
      B = A - 1.E-8*(6487.31 +K*( 58.058 +K*(-0.71150 +K*0.08851 ) ) )
      INDEX2 = ( A*P - B*E ) / T      +1.D0
      dispers=(index1-1.D0)/(index2-index1)
      write(6,*)'Dispersion=',dispers ,' index1=',index1,
     &   ' index2=',index2
      goto 10
      END