A Spectacular Invention

If anyone examine letters or other minute objects through the medium of crystal of glass, if it be shaped like the lesser segment of a sphere with the convex side towards the eye, he will see the letters far better and they will seem larger to him..such an instrument is useful to all persons and to those with weak eyes, for they can see any letter, however small if magnified enough.

Roger Bacon

One of nature’s great inventions is the human eye. Unfortunately it is also one which has a particular biological problem which usually manifests itself around the age of 40. Here the lens begins to harden, a condition which can bring about farsightedness (presbyopia) and cause the organ to no longer be able to focus on close objects. Until the 13th century the only way to cope with this was the use of crude magnifying glasses and crystals. Then in 1285, a breakthrough was made. In 1306 a sermon was given by a Father Giordano de Pisa, in which he said:

‘Not in all the arts have been found; we shall never see an end of finding them. Every day one could discover a new art...It is not twenty years since there was discovered the art of making spectacles that help one see well, an art that is one of the best and most necessary in the world. And that is such a short time ago that a new art that never existed was invented..I myself saw the man who discovered and practiced it and talked with him’

This announcement was probably meant to spread the word outside the monasteries to the general public who could make good use of the invention. The craft of making eyeglasses had evidently been established by a small group of artisans. Pisa at that time had a thriving glass industry with many mirror and drinking glass makers. The inventor himself had chosen to remain secret, probably more out of commercial self interest than personal modesty. The first spectacles produced were simply two magnifying glass handles riveted together and hung on the nose. The convex lenses were manufactured from quartz or beryl. These were difficult to keep in place and several different methods were tried. These included hooking them to a hat brim, attaching them to a plate over the forehead, clamping them on the temples and putting spatula like extensions under that hat. The lenses themselves were probably not of great quality, however they did not have to be particularly accurate to fix farsightedness which simply required magnification.

When printed books arrived, the demand for spectacles increased dramatically. Mass production increased resulting in many primitive poor quality products. In 1465 the Spectacle Maker’s Guild brought in regulation and quality gradually increased. By this time similar guilds had been formed in Germany, France, England, Italy and Holland. In the 15th century, thousands of spectacles were being produced in Florence and Venice and convex lenses had been developed for short-sightedness. The Florentines in particular understood that vision declines with age and manufactured their eyeglasses in batches of five year strengths.

What was so great about this invention?. Well as one commentator recently put it, ‘spectacles have effectively doubled the active life of everyone who reads or does fine work-and prevented the world being run by people under 40’. The invention of eyeglasses had the effect of more than doubling the working life of skilled craftsmen. This was especially true of scribes, readers, instrument and toolmakers, close weavers and metal workers. Fine work and fine instruments could be produced. Scholars and copyists could continue their work and people became accustomed to the idea that human physical limitations could be transcended by human inventions.

David S Landes in 'The Wealth and Poverty of Nations' suggests that the development of eyeglasses and manufacturing of lenses pushed Europeans into other areas and prompted the invention of precision measurement and control devices such as fine wheel cutters, gauges and micrometers. This laid the groundwork for articulated machines with fitted parts. Furthermore the Europeans were beginning to move towards replication and mass production.

Importantly for the history of science, the knowledge of lenses was spreading and opening up new possibilities. In the Low Countries (which became the main suppliers of spectacles to Britain) the microscope and the telescope would be invented in the 1600s and open the door to new worlds.

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