1. Letter on Terrestrial Magnetism, addressed to the Secretary

Abstract

**** I Have the pleasure to send you two papers: the first on the changes, which the moment of a magnetical needle or bar undergoes as a function of the elapsed time, and of the variations of the temperature; the second, in the German language, is an extract of a letter to Professor Kupffer of St Petersburg, exhibiting the changes of the time of 300 horizontal vibrations, in Christiania, of my invariable magnetical cylinder, made by Dollond in 1819, from 1820 to 1839.