Changes in the Length of the Day

Abstract

THE article by Dr. E. W. Brown on “Changes in the Length of the Day” in NATURE of Feb. 5 cannot fail to attract attention. To avoid any possible misunderstanding I think I ought to explain that the references which Dr. Brown makes to my results refer to my paper, “A Solution of Ancient Eclipses of the Sun,” published in the Monthly Notices of the Royal Astronomical Society, Dec. 1920, not to my paper entitled “Trepidation” in Monthly Notices for Dec. 1926, which Dr. Brown had not seen at the time of writing. In the latter paper I show that if we adopt 4.8 as the change in the apparent longitude of the moon in a century, due to any acceleration not recognised in the existing gravitational theory or to changes in the length of the day, the Greenwich meridian observations give 1.36±0.15 as the corresponding change in the apparent longitude of the sun, thus confirming the result which Dr. Brown cites from my work on ancient eclipses. I also find that any correction to the assumed century accumulation for the moon requires a correction of 1/9.5 as much to the deduced accumulation for the sun, so that the latter term is very little dependent on the value obtained for the lunar term.