A drop of pond water comes alive with ancient life: squirming ciliates, algae, amoebae and bacteria. Salt and hair become amphitheatres where you catch an enzyme in action, or watch an embryonic brain hard-wire itself. All these amazing worlds open up through a microscope.
The first microscopes were magnifying lenses that the Assyrians carved out of rock crystal around 700 BC. Much later, in 1600, Zacharias Jannsen of Holland, invented the compound microscope, and it became popular when English physicist Robert Hooke published a collection of sketches of things he saw under it. Modern microscopy came into its own in 1673 when Dutch biologist Anton van Leeuwenhoek achieved a magnification of 300+ with a simple microscope: a single convex lens set between two glass plates in front of which the specimen was placed.
But these early instruments could never magnify more than 2,000 times, as beyond that, the wavelength of visible light is too great to illuminate anything. Then in the 1920s, it was discovered that a magnetic coil could focus electrons moving in a wave pattern similar to that of light, much like a lens focuses light. Max Knoll and Ernst Ruska used this principle to make the first electron microscope, which bombarded the specimen (placed in a vacuum) with electrons instead of light. Its magnification of over a million times enabled scientists to study everything from viruses to cellular structure. The scanning electron microscope, a later avatar, sweeps a focused beam of electrons back and forth over the specimen to create a 3-D view. Modern scanning tunneling microscopes have no wavelength limitations and use an atom-wide probe to scan the specimen and create a contour map.
Recently scientists discovered that green fluorescent protein (a molecule from jellyfish) could be attached to specific proteins in other organisms. These glowing molecules, tracked under a light microscope as they move through living cells and tissues, allow researchers to watch biological processes in real time, in 3-D. These instruments are poised to answer some of the most fascinating scientific questions.