Les instruments du calcul savant > Instruments d'intégration conservés au musée des arts et métiers |
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Orthogonal Planimeter Orthogonal Planimeter with cone-and-wheel mechanism, according to Oppikofer An orthogonal planimeter made by Heinrich Rudolf Ernst (1803-1863) was the instrument which really made known that theoretically exact mechanical integration was possible. Ernst lived from about 1830 onward in Paris. "Ernst's Planimeter" was the usual name for this instrument, thus implying that Ernst should also be the inventor, but this impression would not last for too long (France needed a little bit longer to give up the misleading designation). But there is a pre-history of this instrument, which has to be taken into account. Tito Gonnella (1794-1867), one of the two true and independent inventors of the orthogonal planimeter, had tried in the 1820ies to have certain parts of his instruments made in Switzerland, already then renowned for excellent craftsmanship. The possibility cannot be ruled out that Johannes Oppikofer (1783-1864) came to know around 1826/27 either of one of the instruments or of their construction details, and that he had a planimeter with the cone-and-wheel mechanism built. Oppikofer's instrument was commenced by the mechanic Johannes Pfäffli (1802-1828), finished after Pfäffli's premature death by Ernst around 1828, and presented to the "Berner Naturforschende Gesellschaft" in 1829. (The current whereabouts of this instrument are unknown. Around 1900 it is known to have still existed in Bern). This was how Ernst came to "his" planimeter. It seems that Ernst, when going to Paris, built another copy of the instrument for his own purposes (around 1833/34). He presented the instrument in 1834 in Paris, was rewarded with the Prix Montyon (1837; the instrument was appreciated at this occasion by Poncelet), and received another prize medal in 1839. Arthur-Jules Morin (1795-1880) and, around 1840, Léon Lalanne (1811-1892) made some smaller contributions to the further development of the instrument. Knowledge about the instrument presented by Ernst was widely spread, mainly through an article by the Comte de Lambel, which appeared in the Bulletin de la Société d'Encouragement pour l'industrie nationale. It is probable that at least starting at that time a small production series of orthogonal planimeters began, not limited to Ernst, but divided among several different makers.
Drawing of Ernst's planimeter (from Lambel 1841)
Ernst's orthogonal planimeter, CNAM 02624-0000 It seems that also around that time the legitimacy of Ernst's claim of being the inventor of the orthogonal planimeter was challenged. While the instrument - perhaps the one presented to the Académie des Sciences - preserved in the CNAM's collection bears the simple and clear inscription "Ernst, rue de Lille, 11 Paris", Ernst obviously saw himself obliged to be more precise when signing a probably later instrument of this kind (presently in Aarhus/Danmark) "Inventé par Oppikofer, Géomètre, Perf[ection]n[é] par R. Ernst rue de Lille N 11 à Paris".
Ernst's orthogonal planimeter, detail |
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