Description
"Like a Bos"

This beautiful astrolabe is the first antique instrument in the world to be publicly identified as a forgery. The collector Robert Whipple purchased it in Paris in 1928, taking it to be a rare survival from 16th-century Germany. But when curator Derek Price studied it in the 1950s, he found a troubling anomaly: three other collections in Europe held the exact same instrument, each dated, implausibly, to the very same day, 24 March 1597. Price was able to trace the origin of all of these instruments to a single source in Amsterdam, and soon found dozens more duplicated instruments with this same connection. Collectively, these objects became known as the ‘Mensing forgeries’.

Derek Price began work at the Whipple Museum in 1951 on a project entitled ‘The History of Scientific Instrument Making’. It was his PhD supervisor, Rupert Hall, who put Price on to the question of authenticity. In the Museum's Accessions Ledger, alongside the entry for this object, Wh.0305, there is a note in Price’s hand that reads “Hall says a fake!”

Price soon found several pieces of evidence that confirmed Hall’s suspicions. Wh.0305 matched the description of astrolabes in three other collections in Europe. Chemical analysis of the metal suggested that it was modern—no more than a few decades old. And provenance researched matched 0305’s origin with that of several other suspect instruments.

Price traced all of these instruments back to a single source, the Amsterdam auction house Frederick Muller & Co., which in the early 20th century had been under the direction of the collector and dealer Anton Mensing. Every fake identified by Price was a copy of an instrument sold in two sales run by Mensing. The ‘Bos’ astrolabe and a nocturnal (Wh.0306) were both copied from items listed in a 1924 sale of Mensing’s personal collection. Three more instruments (Wh.1148, 0563, 1149) were copied from a 1911 sale of the Strozzi family collection.

Price did not think that Anton Mensing was responsible for the production of these forgeries. Rather, he noted that at least a dozen of the ‘Mensing fakes’ had passed through the hands of an Amsterdam dealer that he named only as “Mr. X”. Subsequent scholarship has identified this man as Christiaan Feeterse. Tellingly, Christiaan’s brother Jacob was a fine silversmith and artefact restorer who’d been employed by Anton Mensing. It seems likely that Jacob had secretly copied objects from both Mensing’s collection and the 1911 sales catalogue; his brother then sold these copies as genuine pieces.

In December 1955, just as Price was concluding his research into the ‘Mensing forgeries’, another example came to light. It was yet another Bos astrolabe, again dated 24 March 1597, and listed for sale by Sotheby’s of London. Price alerted the auction house to its inauthenticity and the lot was withdrawn from sale. But remarkably the instrument soon passed back into the London trade, where it was sold the next year for a considerable sum to David Wheatland, founding curator of the Harvard Collection of Historical Scientific Instruments.
07/10/2026
Created by: Hannah Price on 07/10/2026

Description
The Whipple Museum was intended from its outset to be first and foremost an academic institution: “a cultural accessory to modern research”.

Since 1944, the Museum has been proud to honour and maintain this legacy. A vibrant Department of History and Philosophy of Science has flourished around the museum. This is just one of the objects from R.S. Whipple’s founding collection that remains a crucial resource for research into past science.

*The 'Mensing' fakes*

In the early 1950s as part of his PhD work, scholar Derek de Solla Price made a startling discovery. Amongst the many gems in the Whipple collection were a small number of forgeries. These were the first fake scientific instruments to have ever been publicly identified. Price explained his findings to R.S. Whipple, who "took it very well, understanding the various dubious points ... when his critical attention was drawn to them." More recently, curators in the Museum have extended Price's work and found at least two more fake pieces.

17/10/2025
Created by: Hannah Price on 17/10/2025

Description
An astrolabe is a model of the heavens with the earth placed at the centre. A section of the heavens is projected on to the astrolabe. The co-ordinates of stars and planets are depicted on a grid called the rete. The earth is represented by latitude plates of which there are more than one. This is because the movement of the stars depends upon the latitude of the place from where the observation is made. Cambridge has a latitude of 52°, Rome 42°, Madrid 41°, and Paris 49°. Each latitude plate has circles and lines engraved on them which include the tropic of Cancer and Capricorn, the equator and a twilight line. The rete and latitude plates are housed within the mather which has a raised edge called the limb. On European astrolabes the limb is engraved with a degree scale showing 0° to 360° and / or a scale of 24 equal hours.

On the back of the astrolabe are engraved several scales including a calendar scale and a shadow square. On Islamic astrolabes extra scales and tables are engraved for finding the direction of Mecca (for times of prayer). At the back of the astrolabe is also the alidade. The alidade has sights through which an astronomer would take simple observations of the sun or of a particular star, to find the time of day or night. The sights can also be used for finding the heights of buildings, trees or hills.

From display label:
This astrolabe purports to have been made by Johannes Bos in 1597, but is in fact a copy of an original from the notorious collection of Anton Mensing. Although most of Mensing’s instruments that have found their way into museum collections worldwide are geniune, a significant number of forgeries have been identified.

Whipple purchased three Mensing objects that are now known to be forged. Generally the best indicator of a forgery is poor execution: in this case the exceptional workmanship of Bos has not been matched; moreover the original of which this is a copy is known.