Berend Wilhelm Feddersen (26.03.1832-1.07.1918) was a German physicist. He was born in Schleswig (now in the Federal Republic of Germany). He studied at the Universities of Göttingen and Berlin, and in 1857 received the degree of Doctor of Philosophy at the University of Kiel. From 1858 he lived in Leipzig, where he edited and published Poggendorff's biographical dictionary (from 1897 as its co-publisher).
His work was in the field of electrical oscillations and waves, the diffusion of gases and magnetism. He studied (1858 — 62) the discharge of the Leyden jar, established its oscillatory character and showed that the period of oscillation is proportional to the square root of the capacitance of the capacitor. He investigated (1859) the ferromagnetic properties of matter in rapidly alternating fields. He discovered (1873) the phenomenon of thermal diffusion.