Bifocals, the combination of both concave and convex lenses for both types of vision correction, a top lens for distant viewing and a lower lens for reading, were developed around 1760 by the American statesman and inventor Benjamin Franklin.

RELATED INFORMATION:
Benjamin Franklin, Inventor Profile   from The Great Idea Finder

ON THE BOOKSHELF:
100 Inventions That Shaped World History
by Bill Yenne, Morton, Dr. Grosser (Editor) / Paperback - 112 pages (1983) / Bluewood Books 
This book contains inventions from all around the world from microchips to fire. This is a really good book if you are going to do research on inventions.
Panati’s Extraordinary Origins of Everyday Things
by Charles Panati / Paperback - 480 pages Reissue edition (September 1989) / HarperCollins
Discover the fascinating stories behind the origins of over 500 everyday items, expressions and customs.
Spectacles and Other Vision Aids : A History and Guide to Collecting
by J. William Rosenthal / Hardcover - 550 pages (May 1994) / Norman Publishing
No other work has covered the field of vision aids on this grand a scale nor provided such magnificent illustrations of such a variety of specimens.
Autobiography of Benjamin Franklin
by Benjamin Franklin / Hardcover / Buccaneer Books Inc; (June 1, 1984)
Franklin's classic Autobiography is his last word on his greatest literary creation -- his own invented persona, the original incarnation of the American success story.

ON THE WEB:
The Franklin Institute Science Museum
A wealth of information on Franklin and Science. Check out the online version of this Philadelphia, Pennsylvania museum.
(URL: sln.fi.edu/)
Ben Franklin's Inventions
A list of Benjamin Franklin's inventions reveals a man of many talents and interests. It was the scientist in Ben that brought out the inventor. His natural curiosity about things and the way they work made him try to find ways to make them work better.
(URL: sln.fi.edu/franklin/inventor/inventor.html)
Compaq.com - Safety and Comfort Guide
Arranging your work area for Bifocals.
(URL: www.hp.com/ergo/)
SPECTACLES: Bacon, Keppler, Franklin, Airy, Fick
Pages Maintained by L.S. Taylor, Electrical Engineering Dept., University of Maryland.
(URL: www.ee.umd.edu/~taylor/optics2.htm)
Benjamin Franklin: A Documentary History
The beginnings of a bio.on Benjamin Franklin. Lots of links to sources for this chronological work.
(URL: www.english.udel.edu/lemay/franklin/introtext.html)
Benjamin Franklin, the American Renaissance Man
Franklin proved the old adage "Necessity is the Mother of Invention" with his creation of the bifocal lens. Another Thinkquest Project site.
(URL: www.thinkquest.org/library/lib/site_sum_outside.html?tname=22254&url=22254/bifocals.htm)
Why Bifocals for Children
From the College of Optometrists in Vision Development.
(URL: www.covd.org/art/bifocals.html)
Learning to Use Bifocals
From the Energy Matters Newsletter By Don Casada and John Kueck, Oak Ridge National Laboratory.
(URL: www.oit.doe.gov/bestpractices/energymatters/mar2000_bifocals.shtml)
Ben Franklin and the Biofocal
Bifocals, the combination of both concave and convex lenses for both types of vision correction, a top lens for distant viewing and a lower lens for reading, were developed around 1760 by the American statesman and inventor Benjamin Franklin.
(URL: www.medgadget.com/archives/2005/07/ben_franklin_an.html)
Tour Philadelphia
Benjamin Franklin invented a device that would forever change the world - the bifocals.
(URL: www.phillyvrtour.org/bifocals.htm)