Multiplying spectacles, 1650.
© Science Museum / Science & Society Picture Library
Multiplying spectacles comprising a pair of rock crystal 'lenses', each with 24 facets, in a gilt metal frame. Spectacles have been in use in the West for at least 700 years. The earliest had convex lenses, and were designed to be worn by people with long sight, to help them focus on nearby objects. Later, concave spectacle lenses were made for people with short sight. In 1784 Benjamin Franklin (1706-1790) invented 'bifocals' - spectacles split into two parts, each with a different focal length.