Leon Battista Alberti, fascinated by ancient Rome, creates a device that would allow him to trace the plan of the old city on any surface. His device, based on a simplified volvelle is a basic gridded circle and a ruler. The circle, which Alberti describes as the horizon and of the diameter the reproducer chooses, is subdivided in 48 even degrees. These degrees are then subdivided in four that Alberti names minutes. The ruler, called by author the Spoke, is also a very simple device. The length of half the diameter of the circle, it is subdivided in 50 degrees. These are also subdivided in four minutes. The two elements, horizon and spoke are joined at the center of the circle by a pin that allows the ruler to revolve 360 degrees.
Joined with the text are a series of informative tables positioning specific points. These points represent corners of walls, gates in fortified walls or landmarks. These points are positioned by placing the spoke aligned with the right degree of the horizon and measuring on the spoke the right degree and minute. This point should then be in the right position in comparison to all other points that will be positioned on the horizon. Playing connect the dots, the points can then be connected by straight or curved lines to create the plan of ancient Rome. Voilà!
The proposed instrument would be one for educational purposes. The horizon would be about 12” of diameter and engraved onto a Plexiglas sheet. The spoke would be made of Plexiglas. The instrument could then be used by drawing the map with erasable colored pens allowing the exercise to be reproduced. The instrument would be a great example of a radial cartography system and could be used to survey other spaces or cities. One could also put to charts the general layout of city based on a printed map.
Other images to come