Talk:Abel Foullon

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How does the Holometer work?

"Other improvements to the instruments being used to perform topographic surveys and maps include a precursor to the plane table, the holometer, (fig. 7) of Abel Foullon, published in Paris in 1551. His description also included the name of the instrument maker from who it could be obtained. The holometer was designed to meet the needs of the practical surveyor who did not possess exemplary skills in mathematics, science, and the use of the technical instruments of the day, making it possible for him to construct the map in the field from direct measurements." Plain Table

"It seems that practical but complacent surveyors, long used to their ways of working, were resistant to newfangled mathematical ideas arising from a resurgence of the art of geometry. The view is widely held today that the average surveyor of elizabethan times could not cope with the simple mathematics required by the geometrical instruments. Out of the surveyor's practical needs comes the invention of the plain table and sight rule, triangulation without arithmetic.

The first step was an instrument called a holometer, devised by Abel Foullon in his book Holometre, Paris, 1551. This book was widely circulated, and was translated into Latin and Italian from its original French. The holometer is a complete field triangulation and plotting instrument; a table for the paper with an inset compass, a brass graduated base line scale on which two arms slide so they can be set a required distance apart for two observation stations, each arm pivots and has sights, etc. It was a cumbersome tool, a reminder of later victorian universal tools which were more bother than help. But the instrument introduced the idea of plotting in the field. And then an unencumbered, plain, table with a sight rule, an alidade and ruler to set on top, was a much more practical step.

The idea is simple. You have a flat table mounted on a tripod stand, in the field, and on this a sheet of paper. There are two fixed stations; which are marked a distance apart on the paper, setting the scale of the map. At station 1 you set up the plain table with the line joining the stations pointing at station 2. With a sight rule, you draw lines out from the plotted position of station 1, each labelled for their target. At station 2 you line up the table again looking back to station 1, then take sights and draw lines to each of the targets. Where corresponding lines cross you plot the target place.

Articolo "olometro" author Camerota, Filippo description: Strumento per rilevamenti architettonici e topografici ideato e descritto dal meccanico del Re di Francia Abel Foullon. Si tratta di una tavoletta quadrata graduata con al centro una bussola e su un lato due linde (v.) graduate munite di visori. A questa invenzione si ispira lo gnomone (v.) di Bernardo Puccini. image descriptions: Fig. in Abel Foullon, Descrittione et uso dell'olometro, Venezia 1564, p. 16; Immagine proviene dall'Istituto e Museo di Storia della Scienza di Firenze. citations from treatises Abel Foullon, Descrittione et uso dell'olometro, Venezia 1564.

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