For Christmas the year I was seven years old my parents gave me a microscope, and I’ve loved microscopes ever since. There’s nothing like your first look at a drop of water teeming with microscopic life, or for that matter your first look at dozens of other everyday things, like salt and hair, magnified a few dozen or a few hundred times. Like books, the microscope reveals a whole new world.
At the Powerhouse of Discovery we have lots of microscopes, because we hold microscope workshops that feature a close-up look at exactly what lives in Wascana Lake. (Believe me, it’s a lively place.) Microscopes, simply put, are fun! But of course they are also one of the basic tools of scientific discovery, and therefore deserving of a place not only in the Science Centre, but in this column.
There are several different kinds of microscopes. The first microscopes were “simple” microscopes–in other words, magnifying lenses. They’ve been around for a lot longer than you might imagine: an Assyrian magnifying lens has been discovered from about 700 B.C., carved out of rock crystal.
The “compound” microscope, using more than one lens, was conceived by Zacharias Jannsen of Middelburg, Holland, about 1600, but the poor-quality glass available caused so much distortion that simple microscopes held their own for years.
In 1665 English physicist Robert Hooke created a sensation with the publication of Micrographia, a collection of sketches of things he had seen under his compound microscope, including fleas and other vermin (with which people of the time were intimately acquainted).
However, the father of modern micrography was Dutch biologist Anton van Leeuwenhoek. In 1673 he created a simple microscope that consisted of a single, almost spherical, lens, set between two glass plates in front of a pointer on which the specimen was placed. Astonishingly, he was able to produce a magnification of more than 300 times with this simple instrument, and was the first person to see bacteria and spermatozoa, and start the long tradition of watching “little animals” cavorting in a drop of water.
Microscopes are needed, obviously, because we can’t see very small objects. Several factors are involved, but one reason is that we can’t see anything that forms an image on our retina smaller than the distance between two light-sensitive nerve endings. (This may be a good thing; we probably wouldn’t really enjoy being able to see all the tiny things, animate and inanimate, floating in the air around us or crawling on our skin.)
A simple microscope can produce an upside-down image of a distant object, such as a light bulb, on a piece of paper held behind the lens at its focal point–the point at which the light rays bent by the lens converge. If the object is moved closer to the lens than the focal length, the image turns right side up and is enlarged, but while our eyes can see it, it can’t be projected on a surface. Instead of being a “real” image, it’s a “virtual” image.
In a compound microscope the objective lens, which is the one close to the specimen, produces an upside-down magnified real image of the object at a point where the eyepiece, acting like a simple microscope, can magnify it into a much larger virtual image that we can see.
Excellent compound microscopes began to appear in the 19th century with the development of lenses free of aberrations and distortions. They proved invaluable in all fields of science, from medicine to biology to chemistry and geology. But no matter how good they got, they suffered one unavoidable problem: they could never magnify more than about 2,000 times, simply because beyond that point the wavelength of visible light is too great to illuminate anything.
But in 1924 Louis de Broglie demonstrated that electrons move in a wave pattern similar to that of light, and in 1927 Hans Busch discovered that a magnetic coil can focus electrons just like a lens focuses light, and in 1930 Max Knoll and Ernst Ruska used this new knowledge to build the very first electron microscope: a microscope that bombarded its specimen (which had to be in a vacuum) with electrons instead of light, and used magnetic coils to focus and magnify that beam onto a fluorescent screen. The possible magnification? Up to one million times.
The electron microscope opened up a whole new level of structure in both animate and inanimate objects. Viruses, invisible before, were studied in detail for the first time, as was the internal structure of cells. Electron microscopy also came to have an important role in materials science.
A more recent variation, the scanning electron microscope, sends a beam of electrons, tightly focused, back and forth over a specimen, creating a three-dimensional view. (The original electron microscope, called the transmission electron microscope, requires a very thin specimen.)
Yet even the enormous magnification made possible by the electron microscope doesn’t represent the end of microscope development. Now there is the scanning tunneling microscope, which uses a probe with a point only one atom wide to scan the surface of a specimen, creating a kind of contour map. It has no wavelength limitation at all. With it, images have been created of a single DNA chain on a carbon field and the pattern of individual carbon atoms in a piece of graphite.
There are other forms of microscopy, too, from fluorescence microscopy to phase contrast microscopy to scanning X-ray microscopy to thermionic emission microscopy. But all of them have one thing in common: they all reveal a new world to us, the world that exists below our level of perception and yet contains the secrets to the structure of our own.
And as I discovered on that Christmas 25 years ago, it’s an exciting world to explore.