The linear astrolabe
The linear astrolabe was invented in the twelfth century as an attempt to construct as simple and as cheap an astrolabe as possible. It is known from manuscript sources, but none survives. Henri Michel was a Belgian collector who compensated for this absence in 1943 by making one of his own in ebony and ivory. It could as easily have been displayed in the 'Possession' showcase to the right of this one, since it represents the determination of the collector to possess the unusual, even where no example exists.
Linear Astrolabe, by Henri Michel, Brussels, 1943 (Inv. 51934)