The microscope

 Without the help of magnifying glass, your eyes see only a limited amount of detail. For example, two dots less than 0.1mm (0.004 in .) Apart blur into a single fuzzy dot. When you consider that many of your body cells are one-fourth the size of the smallest dot you can see, the importance of the microscope becomes clear. By allowing scientist to see what the unaided eye cannot see, the microscope greatly increases the amount of data available for scientific inquiry. 

The light microscope

The microscope most often used in biological research today is the light microscope. This microscope uses light to form an enlarged image of the specimen, or object being viewed.

        The manifying glass, called a simple microscope, is the most basic light microscope. It is a single lens, or curved piece of glass. The Lens  bends light Rays as they pass through it, causing the specimen to appear between 2 and 20 times it's actual size. This apparent increase in the object's size is called magnification. An increase in visible detail is called resolution. The reason for magnifying an object is to allow a viewer to distinguish more details.

The most commonly used light microscope is the compound light microscope, which contains two kinds of lenses. The ocular lens set is positioned near the viewer's eye. It forms part of the eyepiece of the microscope. The objective lens set is positioned near the specimen. Light travels through the specimen and the lenses and into the eye of the viewer.

         The lenses of the compound light microscope determines its degree of magnification. each  lens is marked with a number and the symbol x, which stands for times. Thus. A lens Marked 20 x magnifies an object 20 times. To calculate the total magnification, multiply the power of the objective of the ocular. A 43 x objective and a 10 x ocular can therefore magnify the image of a specimen 430 times. Compound light microscopes are used to view living organisms as well as preserved cells mounted on glass slides.

         Biologists also use a variety of light microscopes. The steromicroscope, used to study large  specimens, has an ocular lens and an objective lens for each eye. This arrangement of lenses provides a three-dimensional view of the specimen's surface magnified 5 to 60 times. The phase contrast microscope clarifies feautures inside living cells. As the beam of light passes through the specimen, the edges of cell structures bend the waves of light. the bent  light waves Cross, or interfere with, the unbent light waves the special lenses of the phase contrast microscope use this interference to reveal  boundaries between cell parts, which appear brighter to the viewer.

             Light microscopes are important tools, but they have one major drawback. these microscopes can magnify an object by any desired amount, but eventually the details of the object become fuzzy. why does this occur?  the resolving power, or the ability of a microscope to provide clear details, depends on the objective lens. The best objective lens can distinguish objects as close together as 0.2 micrometers. A micrometer is a unit of measure that equals one-millionth of a meter (0.000039 in.) By combining this objective with the right ocular lens. The viewer can get useful magnification up to 2,000 times. Resolution at higher magnification is not possible with any type of light microscope.

The electron microscope

Physicists who wanted to solve the problem of achieving higher resolution knew they could do so only by using using an energy beam with a shorter wavelength than that of light. certain atomic particles called electrons have such a wavelength. the electron microscope creates enlarged images with a beam of electrons instead of a beam of light. scientist introduced the first commercial electron microscope in 1935.

         Modern electron microscopes produced both high magnification and high-resolution, but they too have a major limitation. living things cannot be viewed under an electron microscope because they cannot survive the Techniques used to prepare them for viewing. even if they could, they will die in the airless interior of the microscope. the air is removed because electrons cannot travel very far in air. Today scientist used two kinds of electron microscopes. 

the transmission electron microscope (TEM) sends a beam of electron through the specimen. the beam creates a clear detailed image on a television like screen magnified 200,000 times or more.

The scanning electron microscope (SEM) sends a beam of electrons accross the specimen from left to right, a process called scanning. As the beam moves, electrons bounce off the specimen in different dimensions. These electrons produce a three dinensional view of the specimen's surface on a television like screen.