Discussion on longitude differences of catalogues in view of determining ephemeris time

The systematic differences among star catalogues are rediscussed in view of determining the correction to be applied to UT in order to give ET if the Improved Ephemeris (or the moon's ephemeris in the Astronomicat Ephemeris for 1960 on) is used. Discussions concerning the above circumstance in the prediction and the reduction of solar eclipses are given. It is noted that the conventional AT (AT0) is preferable for use in the prediction of solar eclipses. A method of determining ET from the reduction of solar eclipses is discussed.