First half of letter from John Frederick William Herschel, Collingwood to Edward Sabine Herschel thanks [Francis] Ronalds for supply of paper. Refers to Sabine’s discovery about the direction of change in the earth's magnetism, the link to the northern and southern hemispheres, and relates it to suns and other electric currents. Discusses the pressure of an electrical current and developing magnetic forces. In the suns light discusses auroras. Refers to [Heinrich Wilhelm] Dove’s remarks on the globe, ‘superficial temperature and the magnetic force’. Reference to ‘atmospheric electricity’. [This letter is continued in MS/257/2/280]. 10 March 1850