SUBROUTINE AINDEX ( P, T, E, WAVE, INDEX )
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, INDEX, A, B, K, WAVE
C
      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 ) ) )
      INDEX = ( A*P - B*E ) / T
      RETURN
      END