Franklin style spectacles, 1720-1820.
© Science Museum / Science & Society Picture Library
Silver spectacles with round bifocal lenses and sliding side arms made by J Hawkins, Southampton, England. Each lens is made up of two half lenses of different prescriptions. They are from the Dunscombe collection of spectacles at the Science Museum, London. 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.