Part of a Letter from Mr. Professor Euler to the Reverend Mr. Wetstein, Chaplain to his Royal Highness the Prince, concerning the Contraction of the Orbits of the Planets
It is likely that Euler wrote his letter in German, and that this publication is an English translation.
In this paper, Euler says that in order to remove any doubt that the orbits of the planets are contracting continually and their periodic times are consequently reduced, he needs some good ancient observations. He explains that the problem he ran into with Ptolemy's observations is that the times are probably one or two days earlier than the chronologers had calculated. Euler then inquires into whether the length of the day has always been the same. He also argues that the force of Jupiter accelerates the Earth in its orbit so much that the resulting diminution in the length of an Earth year would be too great to be in agreement with observation, unless the diurnal motion had likewise been accelerated in the same proportion. (Based on Eric Aiton's introduction to Opera Omnia Series II, Volume 31.)
Original Source Citation
Philosophical Transactions (London), Volume 1752, pp. 356-359.
Opera Omnia Citation
Series 2, Volume 31, pp.259-260.