The+Lens.+Introduction


 * The Lens **

Not a day passes, not even an hour or a minute or a second, without everyone using lenses, you included. The point is: you don’t see them, because you see through them. These two lenses are right there, in your own eyes. The eye-lens – a small round disk in the central part of the front of your eye-ball - works exactly like a camera lens. Those of us who wear glasses or contact lenses carry an extra set of lenses in front of our eyes to improve vision. Cameras with lenses are everywhere. Most households have at least one lying around. And almost every one in the family except the very youngest and the very oldest have a cell phone with a built-in camera. Lenses are used for many purposes: You can see very (very, very) small things with them, like bacteria or single cells in an organism. That’s what you use a microscope for: to look at the microcosm of the smallest objects. You can also look and see objects that are very (very, very) far: a ship at sea or a plane in the sky, the moon, distant planets, faraway stars... That’s what you use binoculars for and if you must look at a very remote object, you use a telescope: to look at distant objects in the macrocosm. All lenses work on the same principle: a ray of light bends its path when it crosses from one medium to another e.g. from the air into water, or from the air into glass. When the ray leaves the glass again and comes back to the air it alters its trajectory once more. Fill a glass with water, put a pencil in, so that part of it remains above the surface of the water. What do you see? By cleverly bending the surface of the lens on the ‘entrance’ side and the ‘exit’ side, light rays can be bent in such a way that they come together in one point: the focus. If you take a convex piece of glass and find the right distance, the sun’s rays will converge in a single spot. On a clear and sunny day, there will be so many light rays in that one focus that it starts to heat up quickly. If there is anything combustible, after a while smoke starts to spiral upward and before long a fire will flare up. Focus indeed meant ‘fireplace’ in classical Latin, you can guess why. Glass is the best material for lenses, since it is quite hard and stays in shape, while with careful grinding and polishing its surfaces can be given every thinkable rounding. And of course, it lets through light, at an angle. The Egyptians and the Chinese already knew how to make glass and used a curved piece of it to set afire something in its focus. Somebody must have had the idea to hold such a piece of glass in front of an eye so as to magnify whatever was in front of it. The ‘eye glasses’ (spectacles) were born. When you are looking at something close or faraway, the lenses of the eye can adapt themselves to project a sharp picture, they can become a bit more or less concave. This movement is called ‘accommodation’ of the eye. When the eye can no longer accommodate sufficiently a concave (hollow) or a convex (round) lens can correct the curving of the rays so as to make them focus on the correct place in the back of the eye: the retina. All this was known for a long time, all over Europe. There were glassblowers who could handle the glass when it was heated and became fluid, blowing in air to create all sorts of shapes. And there were glass grinders, who would take a piece of solid glass and patiently polish it in the right shape for a lens. Such glass grinders were craftsmen, but learned craftsmen: they had to be very precise, and they had to know just the right curve across the glass, so as to make it suitable for use as a spectacle for a person with particular eyesight. Some of these lens grinders, like Benedict de Spinoza, were famous scholars in their own right, who made some money on the side by grinding lenses (even the greatest minds must eat every once in a while). Of course, they started to experiment with their finely honed pieces. Some of them began putting several lenses together to increase their magnifying effect. That is how the telescope was invented, (literally ‘the far-seer'): Someone put several lenses together in a tube, so as to increase the magnifying effect of each one of them. After some experimentation an instrument was created that allowed the user to see stars that so far had been invisible to the naked eye, and to discern details of known bodies that hitherto had never been seen. But you could also watch birds with them, or more importantly, see the enemy approach from afar. That was, of course, what contemporaries were most interested in, certainly the great commander, prince Maurits of Orange, to whom the Dutch spectacle maker Lipperhey presented his invention in 1608. It is probably one of these telescopes, having tubes made by the silversmith Robert Staes, which is depicted on a painting by Jan Breughel the elder, dated 1611, representing the archduke Albertus of Austria in front of his castle Mariemont, near Brussels (fig. 2).24  It was not all that hard to create the complement of the far-seer: the microscope. But the images of very small things initially were not taken very seriously by the scholars of the day who were more interested in celestial bodies. Work on assemblies of lenses in a tube was carried out in many places at the same time. Maybe the Dutch were the first: Around 1608 there were lens grinders in Middelburg, the capital of the Dutch province of Zeeland and one of them, Lipperhey, came up with a telescope. (the one which he showed to the authorities in the Hague. [Zuidervaart, 2009, 4]). But there was another craftsmen working in the same small street, Janssen, and maybe he was the first to come up with the instrument. Around the same time, many other scholars and inventors were experimenting with assemblies of lenses. As early as 1538, Girolam Fracastoro had placed two ‘eye-glasses’ on top of one another and discovered the strong magnifying effect of the combination. Seventy years later the idea of a telescope must have been ‘in the air’ and experiments went on in England, France, Italy and probably in many other places. To this very day, Dutch historians do not agree who was the first: Lipperhey or Janssen. And when it comes to historians from other countries, they disagree even more about the origin of the telescope. But this is not really what interests us. There is something much more fascinating. All these inventors and explorers were in touch with one another (even as they sometimes tried to hide their discoveries from all too curious rivals and imitators). After the first demonstration of the telescope in the Hague. the news rapidly spread across Europe. A copy of a newsletter with the story printed in the Hague in October 1608 arrived in Paris in mid-November where it was seen by the chronicler Pierre de l’Estoile. He provided it to a publisher to be printed. This Paris-issue was reprinted in Lyon in November, and that very month a copy had reached Paoli Sarpi in Venice. Sarpi passed it onto his close friend in Rome (?) Galileo Galilei, the famous astronomer [Zuidervaart 22]. Galileo probably had a telescope built on the basis of the description and began experimenting with it, adding improvements of his own. With minor modifications the lens alignment for a telescope can be changed so as to make it suitable to look at very small things: a microscope. It did not take long for a telescope to be modified for the observation of things to tiny to be observed wit4h the naked eye. But this microscopic world was not taken very seriously at first. Telescopes were much more impressive since they revealed the mysteries of the heavens above. Only in the 1670s did the Dutch amateur scholar Antoni van Leeuwenhoek surprise the world with his observations of ‘tiny beasts’ (bacteria), spermatozoa and tissue cells. He sent letters about his discoveries - translated in English – to the British Royal Society, where initially no one believed him. But his descriptions of the instruments he used and the things he saw were so exact that the Society’s Members through a similar microscope could see for themselves what Leeuwenhoek had reported: an entirely new world that no one had ever seen before. Princes and scholars from far away came to visit Leeuwenhoek and look through his ocular at tiny objects that had been all around them for all their lives without them ever realizing it. The telescope and the microscope had radically changed people’s perception of the world they lived in: that world was a thousand times bigger than they had ever been able to see, and at the same time there was another world of tiny creatures and structures, a thousand times smaller than they could ever have imagined. And that was only the beginning of the discovery of the macrocosm and the microcosm around us. Yes, ‘man is the measure of all things’, but these things may be endlessly larger than a human being, or infinitely smaller. Through the telescope and the microscope scholars had seen a new reality that no philosopher had ever thought of. Scholars decided that it was not enough to sit in one’s armchair and reflect upon the wisdom of the ancient sages. They had to go out in the real world and see for themselves, use the new instruments or sail to unknown coasts to discover what that world was really like. The scientific revolution had begun. This occurred all over Europe. In many places glass grinders and scholars constructed their own instruments, often following foreign examples that they had encountered on their travels abroad, or read about in newsletters. With their new tools they observed the vast skies and tiny droplets of water or blood. They reported their discoveries to other researchers and learned from them about the latest discoveries elsewhere. Yes, there were great geniuses, epochal discoveries. But mostly, there were hundreds, maybe thousands of curious scholars who wrote and visited one another, learned from one another, and in doing so, in the course of centuries, together wove the web of science all across Europe, and beyond. But what happened in your area? When was the telescope or the microscope first used and what discoveries were made with them? Tell us about the threads that were spun to connect to the great web of science in your part of Europe