HUMBOLT (Fr. Alex. de). EXPERIMENTS ON GALVANISM and in general on the irritation of muscle and nerve fibres. Paris, printed by Didot jeune, 1799. In-8 of 46-530-[2] pages, half tan basane, untrimmed (contemporary binding). ORIGINAL EDITION of the translation illustrated with 8 folding plates. Copy enriched with a very interesting signed letter from the author to M. Mathieu: "I am afraid you are wasting your time with my invariable pendulum, made of copper with a lead-filled lens. I received it too late to carry out the experiment in Europe; I intended to do it before arriving in Mexico... (He then gave a series of observations).