Early History of Microscopy

The Invention of Early Microscope

Single microscope: A single microscope is a single lens (also called magnifying glasses) forms a virtual image of the speciment on the retina of the eye. This single lens can be used to produce an enlarged real image in space, like on the sheet. Lenses of this sort had been made since at least the 14th century.

Compound microscope: A second lens is used as a magnifying glass to view the real image. This is invented around 1600. Actually telescope has also been invented almost at the same time because telescope at that time was also a combination of two lenses (depends on the sizes of the lenses and their relative spacing).

The interesting thing is that the telescope was made immediately afterwards the 1600s discovery, which had been used to discover the craters on the moon and the satellites of Jupiter by Galileo, there is almost no info gleaned by the use of microscope though.

Robert Hooke and Cell

In 1665, Robert Hooke published a magnificent book called Micrographia, showing different types of objects (mostly biological in nature) taken by a compound microscope. One of the most famous images is the image of cork cells, which is always used as illustrating the discovery of cells.

But, the fact is that he was actually referring to a cell in the simple sense of a box (like some kinds of square objects), not that he had any concept that tissues of animals and plants are composed of what we now know as cells. So, it’s a little bit misleading to say that he discovered cells.

So, this is 65 years after the so-called invention of the microscope. But why did it take such a long time?

This is because all lenses that were possible to grind at that time in the 17th century have either a spherical surface or a plane surface, which only form a good image near the center. And if you put two lenses together as compound microscope, they have more spherical abberation than one lens.

So Robert Hooke can use this microscope to see objects like flea, but to see even smaller objects, the lenses had to be made smaller and it’s better to go back to simple microscope to get a more clear image of very small object.

That’s why the highest magnification objects that were looked at at that time were actually looked at with simple microscopes not compound microscopes.

Leeuwenhoek and Simple Microscope

The most famous of these simple microscopes was the microscope used by Leeuwenhoek. It’s a quite complicated microscope which has a very tiny single lens and one needs to put it right up to his eye to see the image. But it turned out that it produced a much better image than a compound microscope at that time.

And so Leeuwenhoek was able to see bacteria, protozoa, cilia, flagella and sperm for the first time.

So, the most important advances in observing small biological objects came with simple microscopes, not with compound microscopes. Even as late as 1830, the best observations on cells were being made with simple microscope.

In and After 19th century

These problems with chromatic and spherical abberation were first addressed in the 19th century, and so it really wasn’t until the 19th century that compound microscopes became better than single microscopes.

And with the improvement of optical techniques, the cell theory was first enunciated by Schleiden and Schwann in 1838.

So the 19th century was really the time when it was discovered how to fix cells and tissues, how to embed and stain them to see the different parts. And the chromosomes, mitosis, and so on were only discovered in the latter part of the 19th century, when the compound microscope in fact came to its perfection.

For example, Abbe had achieved resolution which actually matched the theoretical limit in 1888, and microscopes really have not, until very recently, exceeded the limit set by the type of microscope that Abbe invented.

This post is a short summary of this Youtube video below. You can check out it for detailed explanation!