def calc_dt_before_1900(y)
      t = y - 1860
      dt  =  7.62          + \
           ( 0.5737        + \
           (-0.251754      + \
           ( 0.01680668    + \
           (-0.0004473624  + \
           ( 1.0 / 233174.0) \
           * t) * t) * t) * t) * t
      return dt
    rescue => e
      raise
    end
def calc_dt_before_1900(y)
      t = y - 1860
      dt  =  7.62          + \
           ( 0.5737        + \
           (-0.251754      + \
           ( 0.01680668    + \
           (-0.0004473624  + \
           ( 1.0 / 233174.0) \
           * t) * t) * t) * t) * t
      return dt
    rescue => e
      raise
    end
=========================================================================
 deltaT (1860 <= year && year < 1900)

 @param:  y   (Year coefficient for deltaT calculation)
 @return: dt  (sec)
=========================================================================