When the Ashmolean Museum moved to its present site in Beaumont Street, its original building in Broad Street became home to the world's first Museum of the History of Science.

It holds the world's finest collection of medieval and Renaissance scientific objects. Sometimes we don't appreciate what we have on our doorstep!

Dr Jim Bennett's task when taking on the role of director in 1994 was to find a balance between the museum's academic and public functions. He has since mounted a succession of successful exhibitions and family-friendly activities as well as many fascinating public lectures.

We asked him to pick just one exhibit to take with him to the desert island.

Jim said: "There are a number of famous objects that are very tempting. We have the only spherical astrolabe in the world. It is Islamic, beautiful and unusual, but it was essentially a bad idea. The reason that there is only one is because it was a failure! It is unlikely that any more were made.

"The astrolabes that succeed are flat like maps. One of the most famous is here. It was presented to Elizabeth 1 by its maker Thomas Gemini. He was a shrewd businessman because Gemini was not his real name. England under Elizabeth had ambitions to become a world power but our knowledge of mathematics was poor. That knowledge was brought here by immigrants like Thomas, who came from the Netherlands.

"He set up shop in London and since no-one could pronounce his name correctly and he made scientific instruments, including astrolabes, he called himself Gemini.

"Another famous exhibit is the large elaborate silver microscope made by George Adams for George III. It is superb but also absurdly over the top.

"But I shall leave all these celebrated items behind and chose one of the most obscure. I will take this wooden Horary Quadrant. It will be very practical on the desert island because as long as I know the date and the latitude. I can use it to tell the time anywhere in the world. They remained in use until the invention of the radio. A watch can tell the time but cannot find the time, and there was a need to find the time in order to set a watch.

"This piece of advanced technology was made in 1558. It is particularly special for me because I researched its origins myself. I shall be able to recall that journey while I am on my desert island. It is part of the collection of Louis Evans which founded the museum and he purchased it in a shop in Paris.

"It is rare, not because it was rare at the time, but because it has survived. The ones made with metal were treasured and preserved, but most humble wooden sundials like this one perished.

"One side finds the time in Italian hours - this was the first clue to its origin. It is inscribed (in Latin) Miniato Pitti of Florence made this'. I traced him to the monastery of San Miato al Monte of the order of Monte Oliverto in Florence.

"I visited the monastery where Pitti had been Abbot - they knew all about him. They told me he was a nobleman related to the family who owned the Pitti Palace and was close to Cosimo Medici.

"Powerful men often signed pieces, but didn't actually make them. In this case, according to monastery records, Miniato enjoyed engraving them with his own hands. In this example he made a small error. On one side he carved, in Roman numerals, MDLVIII', but on the reverse he missed out the V' and scratched it in above when he noticed his error.

"He was obviously a Renaissance man because his interest was in both the arts and sciences. He arranged the map room in the Palazzo Vecchio and befriended Giorgio Vasari, helping him find a publisher for The Lives of the Artists.

"His letters to Vasari mention conversations with Michelangelo. So as I hold this quadrant I am not only in touch with the man who engraved and coloured it, but also with the great Renaissance artist and writer. I can imagine him, his life and the people he met and maybe wonder how it ended up in the shop in Paris. There is plenty to hold my interest, for it is both technically challenging and aesthetically pleasing.

You can see the Jim's Horary Quadrant in the Museum of the History of Science, Broad Street, Oxford, open Tues -Fri, noon-4pm, Saturday, 10am-5pm and Sunday, 2-5pm. Admission Free. The current exhibition, Small Worlds - the art of the invisible, runs until until April 6. To subscribe to a free mailing list and receive news of museum events by e-mail visit the website: www.mhs.ox.ac.uk