A brief History of the Microscope
Oddly enough, the compound microscope was invented before the single lens microscope. But the instruments were not very good to start with and much more could be seen with very small lenses of short focal length.
In about 1597 two Dutch eyeglass makers, Zaccharias Janssen and his son Hans were experimenting with lenses in a tube. They observed that nearby objects viewed through two lenses in line were magnified. Their device was the first compound microscope. However, their lenses were rather large and the magnification obtained was only about 10X. Galileo also designed a compound microscope, but it was only useful for reflected light. Robert Hooke built the first useable British compound microscope in about 1655.
The single lens microscopes made by a Dutch amateur lens grinder Antonie van Leeuwenhoek were far superior to the early compound instruments. Van Leeuwenhoek, in about 1670, developed a method for grinding very small glass lenses. They were tiny, of the order of a millimeter in diameter, and could magnify several hundred times. Mounted in a brass plate these lenses could use transmitted light to image objects in a drop of water on the end of a metal pin. Screws were used to move the pin and focus the specimen. Van Leeuwenhoek was probably influenced by Robert Hooke’s Micrographia (1665) which he might have seen when he visited London in about 1668. Amongst his vast number of discoveries were bacteria, sperm, blood cells and a myriad of protozoa. He also laid the foundations of plant anatomy. His discoveries were reported to the Royal Society in a series of famous letters. Van Leeuwenhoek made hundreds of microscopes over the years and many people copied them, including Hooke himself. Nine of van Leeuwenhoek’s original microscopes still exist today.
Hooke confirmed Van Leeuwenhoek's work and one of the important discoveries he made with his own compound microscopes was that of the cell. He examined the structure of cork. At that time cork was a very valuable commodity for the English ship building industry. He found that cork was made up tiny chambers that he called cells, coining the term to describe what we know today as the building block of all animal and plant life.
Minor mechanical and optical improvements were made to compound microscopes over the years, but no major improvements were made until the 19th century. In 1847 Carl Zeiss started making simple microscopes in Jena, Germany. By 1857 he was producing a compound microscope, the Stand I. The business grew and in 1872 Ernst Abbe joined the firm. Abbe worked on optical design and this led to the discovery of many basic facts about optics and lens design. After Otto Schott, an optical glass expert, joined the firm in 1886 the lenses produced by Zeiss soon became the best in the world. Apochromatic, Planapochromatic and Immersion lenses originated in the Zeiss laboratories. Compound microscopes were soon being made all over the world and Germany, Great Britain and the USA led the market. Hundreds of different designs of microscope appeared, especially in the USA and Great Britain and in such a short article it is impossible to deal with them all.
There have been great advances made over the last 70 years and firms such as Zeiss, AO Spencer, Vickers, Leitz, Wild, Reichert, Nikon and Olympus and many others have produced a vast selection of different kinds of light microscope. Some of these will be described in the other sections.
The Electron Microscope was invented by Ruska in 1933 and the first commercial instruments came from the Siemens factory in Berlin in about 1937. An Electron Microscope which employs a focused beam of electrons instead of light to image the specimen is capable of far greater magnification and resolution than a light microscope. Resolution in the Light Microscope is limited by the wavelength of the light used and is usually about 250 nanometers, or millionths of a millimeter. The wavelength of the electron is far shorter and resolutions of 0.3nm are routinely possible at magnifications that go to 1 000 000X. Later the Scanning Electron Microscope was developed and in 1980 the Scanning Tunneling Microscope and variations. These will all also be discussed in later sections.