Published online by Cambridge University Press: 12 April 2016
Bessel was not able to detect significant latitude variations in his observation series made between May 1820 and June 1821 at Königsberg Observatory. He left the topic until July 22, 1843, when he suspected that the latitude might have changed since 1820. Between March 1842 and April 1843 Peters, one of Bessel’s students, performed an observation series of the pole’s zenith distance at the Pulkovo Observatory using new observation techniques and reduction methods first developed by Bessel. From this series he deduced a significant value of 0″.079 ± 0″.017 for the amplitude of polar motion, but he was not able to separate the expected 10 month Eulerian period from an annual signal possibly caused (as he supposed) by seasonal temperature variations. Peters’ successors at Pulkovo, Gyldén and Nyrén, continued to observe latitude. Using these observation series Nyrén derived in 1873 significant values for the amplitude of polar motion, but he was not able to determine the phase angles because he assumed the period of polar motion being known. We conclude that Peters probably was the first one to have observed a variation of the latitude, but that he and Nyrén were misled by the Eulerian period when modeling polar motion.