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Inventory no. 47493 - Former Display Label


Gilt brass and blued steel. Unsigned and undated.

This is a version of the 'Radio Latino', a surveyor's triangulation instrument devised before 1583 by Latino Orsini, and described by him in his Trattato del Radio Latino, Rome, 1583 and 1586. Earlier instruments incorporating the same basic idea are known, however (e.g. the triangulation and dialling instrument by A. Descrolieres, 1579, also shown in this case).

The 'Radio Latino' consists essentially of a central arm to one end of which are attached two hinged arms. These arms are also hinged, by means of two smaller arms, to a slider which moves over the central arm. In this instrument, the two main side arms are pivoted by an ingenious device involving a sprung steel grip (shaped like a tuning-fork) which holds the steel knife edges, at the end of each arm, in contact with each other. The central arm is engraved with a scale indicating the various positions of the slider for drawing polygons of up to fifteen sides, with the aid of the two side arms. This scale is marked with transversals for use with a scale on the slider subdivided into ten parts; in this way the instrument may be used to construct irregular fortifications, etc., with internal angles of which 360 is not a multiple. Mounted at the free end of the central arm is a rotatable compass (magn. decl. c.10° E. = c.1595) with an index attached at the side which moves as the compass is turned over a scale of 360°. Over the compass glass is a small string-gnomon horizontal dial for latitude c.48° (probably Augsburg). Underneath the central arm are engraved two scales: a trigonometrical scale of 360° (a more precise alternative to the scale of polygons on the upper surface of the arm), and a scale of "Wiener Zoll [Inches]". (To use the scale of degrees, the instrument must be disassembled and the arm reversed.) On the smaller side arms are scales of "Prager Zoll" and "Romer Zoll".

One of the uses of the scales of polygons on this and many other topographical instruments was in the surveying and drawing prior to the construction of the polygonal military installations (e.g. defending walls) favoured in the sixteenth, seventeenth and eighteenth centuries. Scales of polygons were also "contrived for the ready division of the circumference of a circle into any number of equal parts".

Billmeir Collection

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