ALS in German, signed “M. Planck,” one page both sides, 5.5 x 8.75, October 5, 1897. Handwritten mathematical letter to Dr. Ludwik Silberstein, discussing the full solution (the "general integral") of a particular differential equation. Well known for his mathematical prowess, Planck obtains the solution, both in general, and in a particular “limiting case” of interest to Silberstein. He adds a postscript (translated): "The proceedings of the Physical Society in Berlin are sent free of charge only to dues-paying members." In very good to fine condition, with a partial split to the central horizontal fold, a few tiny edge tears, and a diagonal crease to one corner.
