Apart from the Sextant which was an absolute must for the resolute traveller to remember when to phone home and also to be able to record exactly where he or she was - this category is the home of the Orreries. I cannot eulogise enough about these hand made, glowing, moving, brass representations of our Solar System. With revolving cogs and shadows cast you can marvel as you unravel the mysteries of the movements of the spheres. Actually there aren't any spheres - I think modern science disproved that and went for ellipsoids?