Historians disagree about the origin and the use of demonstrational armillary spheres, partly because the available evidence is difficult to interpret.
Very few examples of the instrument survive from earlier than the 16th century. This may be due to their fragile nature and the materials used to construct them. Delicate spheres composed of rings, even when these were made of brass, are less likely to have been preserved than flat instruments such as astrolabes.
While there is a good deal of evidence suggesting that ancient and medieval armillary spheres existed, much of it is not straightforward. Medieval texts often refer to instruments that could be either armillary spheres or celestial globes. Texts that specifically mention the construction and use of armillary spheres seem to be less common than those that deal with other astronomical instruments.
Spheres and globes
It seems likely that the uses of demonstrational and observational armillary spheres were closely related. Ancient astronomers such as Claudius Ptolemy and medieval scholars working within the Islamic world wrote about observational armillary spheres that were larger than demonstrational ones. Demonstrational armillaries were clearly known in Western Europe from the later Middle Ages onwards, and were commercially produced in the 16th, 17th and 18th centuries. Like globes, they are still produced as ornaments for the home, as garden furniture, and as monuments.
