For thousands of years humans have been exploring their environment in an attempt to explain the world around them. Our observation, however, was limited by what we could see with the naked eye. The invention of microscopes widened the scope of human understanding, contributing to countless scientific discoveries in the fields of biology, botany, forensics, entomology and more.
Microscopy began at first by observation of the properties of glass and water to distort or enhance an image. In the 2nd century B.C.E., Ptolemy observed that a stick in the water appeared to bend, and used the angle of the stick to calculate the refraction constant of water almost exactly.
In the first century after the invention of glass, Romans observed that a glass which has a center thicker than its edges would have a magnifying effect.
Around 800 years later Ibn al-Haytham, influenced by the work of Ibn Sahl’s studies of light refraction, described the properties of the magnifying glass in his Book of Optics.
Translations of the Book of Optics led to spread of this knowledge in Europe, resulting in the development of eyeglasses by Salvino D'Armate in Italy in the 1200’s
In the late 1200’s Roger Bacon, an English Franciscan monk, is credited with being the first to combine two lenses to improve magnification, inspired by the work of Ibn al-Haytham.
At this point technology was limited to single lenses usually with a magnification power of 6-10x.
The First Microscopes:
In the 1590’s two Dutch spectacle-makers, Hans Jansen and his son Zacharias Jansen, were credited with creating the first microscope by experimenting with two lenses placed in an extendable tube instead of just a single lens. Although the image was greatly enlarged it was still not much better than the magnifying glass because the image was very blurry.
GalileoGalilei created a microscope with both a concave and a convex lens in 1609.
In 1625, Giovanni Faber coined the term microscope after seeing Galileo’s invention
Antony Van Leeuwenhoek (1632-1723) was the first person to create a practical microscope; it was handheld and only had a single lens. He developed ways to make stronger lenses by more precisely grinding the glass. This enabling him to see things that no one ever had, such as blood cells, yeast, and bacteria.
In 1667 RobertHooke, credited with creating the first truly functional two lens microscope, published Micrographia. This was a collection of biological micrographs including beautiful illustrations of fleas as well as other microscopic creatures. He also coined the term cell after observing a magnified portion of cork.
Development of the Modern Compound Microscope
For about 200 years little improvement was made, and the “chromatic effect” (halos obscuring your view due to the refraction of light) still kept microscopes from giving the clear images they do today
In 1826 Joseph Jackson Lister created the first modern compound microscope using an achromatic lens, which began to resolve issue of the chromatic effect. The lens helped to resolve light wave disparities, clarifying the magnified image through the use of one convex and one concave side of a lens. The manufacture of these lenses was done by trial and error, so the science of microscopy was still inexact.
Ernst Abbe, in the 1860’s discovered the Abbe sine condition, which was a formula to calculate the precise measurements required for a lens to get the clearest image possible at the maximum magnification
Light microscopes continued to advance with more exact lens manufacturing skills, however no major advancements in design have occurred
Limitations in light microscopy eventually led to the invent of electron microscopes, however for most common purposes the compound light microscope is still the standard
The cause of tuberculosis, cholera, and multitudes of other diseases
The mammalian ovum (egg)
How reproduction takes place on the cellular level
Theory of the Microscope
How do lenses work?
An image is stretched, and inverted, when it passes through a concave lens.
Lenses work by harnessing the power of refracted light. Refraction occurs when light (or any other wave such as a sound wave) passes through a substance with one density to a substance with another and becomes distorted. This is easily observed when you look at a straw in a glass. You can see how the straw appears to bend. This distortion can be used to magnify by accurately shaping the lens, in order to “stretch” the image. The light is now bent into a large image, so when it hits the lens in your eye, the original image has become magnified.
How do microscopes work?
Microscopes work by using light and multiple lenses to create a highly magnified image. Light from below the specimen travels through a concave lens, what is known as a condenser. This focuses the light onto a small area of the specimen. The light (and the image) then hits the objective lens. There are usually three objectives with differing powers of magnification (4x, 10x, and 20x). It is focused onto the eyepiece lens where it is magnified again by 10x. Using multiple lenses results in magnifying the image further. The total magnification is calculated by multiplying the magnification factor for each lens. Viewing an image under the 4x objective lens will result in a 40x image after passing through the 10x eyepiece.
Why do you need to focus the image?
Here, at the focal plane, the image is focused and clear
Adjusting the focus knob on a microscope moves the lens back and forth, shifting the focal point, allowing the microscope to focus on different planes.
What is the Purpose of Visikol®?
As we went over earlier when we talked about the lens, refraction is a change in the direction of a wave caused by the medium it is passing through. The refractive index of a material is a measure of the degree that light is bent (refracted) by passing through the material. In microscopy, refraction occurs when the light waves pass between the medium and the specimen, causing blurring and distortion of the image. Visikol™ has a refractive index which is very close to glass, so when the light passes through the glass slide, into the Visikol™, and through the specimen (which has absorbed Visikol™ into it), it does not bend much at all. The light can then make it in a straight line to your eye, so that there is no distortion and blurring.
Microscopes in Action
Basil leaf which has been infected by Downy Mildew—notice the black spores and tendrils.
Fruit Fly (drosophila) depicting eye, leg, wing and legs—notice the tiny hairs on the eye, known as setae
Grains of sand—notice the color changes caused by differences in the refractive index of the sand