Kleist, Ewald Georg von

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Kleist, Ewald Georg von

(b. probably Prussian Pomerania, ca. 1700; d. Köslin [?], Pomerania [now Koszalin, Poland], 11 December 1748)


Kleist’s father, a district magistrate (Landrat), sent him to the University of Leiden to prepare for his place in the Prussian administrative squirearchy. He returned, with an interest in science, to become dean of the cathedral chapter at Cammin and a member of the high court of justice (Hofgericht) at Köslin. Kleist’s only recorded researches concern electricity, which he began to study in the mid-1740’s, inspired by the electrical flare (the ignition of spirits by sparks) and the spectacular displays introduced by G. M. Bose.

Kleist began the experiments which culminated in the invention of the condenser with attempts to increase the strength and reliability of the flare. It appears that he tried to build a portable model, and to this end he placed a nail in a “narrow-necked medicine glass” containing alcohol as fuel. He was quite unprepared for the shock he received when he grasped the nail after touching it to his electrical machine. “What really surprises me”, he wrote to J. G. Krüger, a professor at Halle, in December 1745, “is that the powerful effect occurs only [when the bottle is held] in the hand. . . . No matter how strongly I electrify the phial, if I set it on the table and approach my finger to it, there is no spark, only a fiery hissing. If I grasp it again, without electrifying it anew, it displays its former strength”. Apparently Kleist had held (that is, grounded) the bottle while charging it, thereby transforming a simple conductor (the nail) into the positive coating of a condenser.

In the winter of 1745-1746 Kleist reported his discovery to several German savants, but without specifying clearly the necessity of grounding the bottle’s exterior during charging. None of his correspondents succeeded in reproducing his results. The general theory of electricity accepted at the time, which assumed that electrical matter could traverse glass of the thickness of bottle bottoms, counterindicated Kleist’s arrangement for concentrating electrical force; it was not until Pieter van Musschenbroek described more exactly a similar chance experiment done at Leiden toward the beginning of 1746 that others could confirm Kleist’s claims. Their subsequent discovery that the shock from the Leyden jar (or Kleist vial) was the greater the thinner the bottle was (that is, the larger the theoretical leak), dealt a deathblow to the traditional approach, cleared the way for the Franklinian system, and won Kleist a foreign membership in the Berlin Academy of Sciences.


Kliest’s letters describing the invention of the condenser appear in J. C. Krüger, Geschichte der Erde (Halle, 1746), pp. 177-181; and D. Gralath, “Geschichte der Elektricität [II]”, in Versuche and Abhandlungen der naturforschenden Gesellschaft zu Danzig, 2 (1754), 402-411.

Biographical details will be found in Allgemeine deutsche Biographie (repr. Berlin, 1969), XVi, 112-113; and A. von Harnack, Geschichte der königlichen preussischen Akademie der Wissenschaften, I, pt. 1 (Berlin, 1900), 474. On the condenser see J. L. Heilbron, “A propos de I’invention de la bouteille de Leyde”, in Revue d’histoire des sciences, 19 (1966), 133-142; and “G. M. Bose: The Prime Mover in the Invention of the Leyden Jar?”, in Isis, 57 (1966), 264-267, and literature cited there.

John L. Heilbron

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