Text 2. The glass lens

Many of the scientific advances that have shaped the modern world were possible only because people devised tools to improve their ability to see. The development of glass lenses, which can be used to see things that are either very small or very far away, has had profound consequences for humanity.

The first application of ground, or polished, pieces of glass was not for the microscope or telescope, however, was for spectacles (eyeglasses), which improve the vision of people with imperfect eyesight. It might be argued that without the invention of spectacles, printing would have taken much longer to catch on. Most people become farsighted as they age, and printed material held near the face dissolves into a blur. Without corrective lenses reading becomes frustrating, if not impossible. The first spectacles were invented in Italy in the late 13^th century although crude versions may have been used in China several centuries earlier.

It took several hundred years before anyone assembled glass lenses in a way that made distant objects appear close. The credit for the invention of the telescope goes to Dutch optician Hans Lippershey. In 1608 Lippershey demonstrated his "looker" for the Dutch government, which immediately grasped its usefulness as a military tool. The next year, Italian physicist and astronomer Galileo used an improved version of Lippershey's invention to study the sky. Galileo's telescope could magnify things to 20 times their actual size. With this instrument he observed moons orbiting Jupiter, which contradicted the prevailing belief that all heavenly bodies revolved around the Earth. Galileo's observations helped initiate the scientific revolution that has fundamentally altered our world.

Early-17^th-century Holland was a hotbed of optics development. It was here around the year 1600 that the microscope was invented, although sole credit for this achievement is difficult to determine. By 1625 optical workshops had been set up to build these new instruments, and in the late 1600s scientists were using microscopes to observe teeming microbes in a drop of water and the physical structure of living cells. These and other microscopic discoveries transformed biology. It was also during the l600 that Dutch naturalist Antoni van Leeuwenhoek built his own microscope and discovered what he called animal' cules, which are now known as bacteria and protozo. Much of our knowledge of disease and how to fight including the concept of immunization, has flowed the use of the microscope.

Exercise 1. Make up a list of inventions which are of benefit to humanity in terms of healthcare. Who invented them?