Microscopy
Microscopy is the study of items using a microscope, a device designed to make small things appear larger.
There are several different forms of microscope available to the researcher in a modern laboratory but all owe their origin to the microscopes that used optical lenses to enlarge objects. The first record we have of an artificial lens being used for magnefication dates from 1267. Roger Bacon's work Perspectiva described viewing minute objects through a lesser segment of a sphere of glass or crystal to enlarge them. Spectacles were in use shortly after this period to correct vision and enlarge objects, but it was not until 1595 that the first device that could truly be considered a microscope was made. This microscope was prepared by Zacharias Jansen (1580-c.1638) in Holland. This was the first compound microscope in that it employed two separate lenses that could be moved relative to each other by the means of a sliding tube. This allowed the microscope to zoom (to change its magnification) from 3x to 9x. This system was eventually improved by Robert Hooke (1635-1703) who added a third lens attached to the viewing (eyepiece) lens. This was carried out using an eyepiece from a telescope, an optical instrument with a longer pedigree than the microscope. Once the first Jansen microscopes had been made word spread rapidly throughout the world and the seventeenth century saw many microscope manufacturers and users appear. It was at this time that the word microscope was first used by an Italian scientific society which included Galileo (1564-1642) as a member.
Some of the early work that was carried out using these primitive microscopes is still highly regarded today. In 1660 Marcello Malpighi (1628-1694) was able to prove the blood circulation theories of William Harvey (1578-1657) by discovering the presence of capillaries connecting arteries and veins in the body as well as identifying many microscopic structures in the human body. Some five years later Robert Hooke (1635-1703) published the first pictures of the cells making up living organisms. Prior to these works it had been assumed that the microscope was nothing more than a toy. At this period some microscopes were 2 ft in length and illuminated by oil lamps.
A Dutch amateur scientist named Antoni van Leeuwenhoek (1632-1723) is often credited with the first microscopes. In fact Leeuwenhoek was merely capable of making better lenses than anyone else which made his instruments more effective, he was able to produce magnifications from 50x to 200x with excellent resolution. He made the first observations and descriptions of bacteria, protozoa, and spermatozoa. This is all the more incredible when it is considered that Leeuwenhoek had returned to using only a single lens. It was not until the 1800s that compound microscopes were capable of similar resolution. The period from then until the late twentieth century has seen much improvement both in the mechanics and optics of microscopes. Of particular problem has been aberration - distortions introduced by the lenses themselves. It is often necessary to introduce new lenses to correct faults in other lenses.
Modern light microscopes are capable of a maximum magnification of something in the order of 1,500x, this is achieved by viewing the subject through oil which allows better transmission of the light into the glass of the lens which it is in contact with. This technique is called oil immersion.
For higher magnifications other instruments and techniques must be used. To overcome the limit of the compound light microscope electrons were the first successful alternative. It was in 1932 that the electron microscope was first developed. In many ways it is similar to the light microscope, with the exception that electrons are used to view the image and the electrons are focused by electronic fields and magnets rather than glass lenses. This development led to magnifications in the order of 500,000x. Because electrons are not visible to the human eye the eyepeice is replaced by a television screen.
The next development in the microscope field was towards the end of the twentieth century when the atomic force microscope was developed. In rapid succession the field ion microscope and the scanning tunnelling microscope soon joined these microscopes. This latter device is capable of such magnifications and resolutions that groups of atoms can be visualised. This group of instruments can magnify 1,000,000x and they generally work by measuring distortions in electric fields around atoms.
Microscopy is a fascinating subject which has quite literally given us a whole new view of the world. In the 400 years since the field started massive advances have been made, both in terms of what is technically possible and also in what can be discovered using a microscope. During the last 50 years of the twentieth century the reliance on light and light microscopes has reduced. The twenty-first century will hopefully open up new ways of looking more closely at the world.
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