A Model Solar System.

This is my favourite exhibit at The National Museum of Scotland: an exquisitely-made German orrery, enclosed in a great glass globe. The first orrery was named after The Earl of Orrery, for whom the first mechanical model solar sytem was made in 1704, and this fine example was produced in Munich by Michael Sendtner, and is 98 years old.

I used to be fascinated by the clockwork gearings that would whirr and click when operated electrically by a pedal on the floor, the model planets would begin their stately model orbits around the solar globe - Earth, Mars, and the outer planets even had tiny moons whizz around; the Galilean Satellites of Jupiter would demonstrate their appearance in binoculars if you looked at the right angle, shuttling around Jove's great globe.

The Museum is opened it's doors again to the public today after a £47.1 million, three-year refurbishment programme, but after all that, this beautiful machine still doesn't work.