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The Microscope

Microscopes of one kind or another had been around since the seventeenth century where they had been used both as scientific instruments and as the playthings of the rich in their search for after dinner entertainment. But by the opening of the nineteenth century there was considerable frustration with the physical phenomenon of magnification.

The simple, single lenses then used in microscopes, would bend light rays coming from an object and would produce a magnified image if the arrangement and bending of the light was correct, but the image would always be fuzzy and out of focus, making detailed observations impossible. The reason was not hard to find. Light rays hitting the outer edge of a lens are bent 'asymmetrically' (meaning 'not-the-same'), and come together at slightly different places. The effect is to produce a fuzzy, out of focus image no matter how hard you try. White light also has many different colors and different colors of light focus at slightly different places, producing colored fringes around an object and messing up the image even more.

The person credited with correcting both these problems was a London wine merchant by the name of Joseph Jackson Lister. What Lister did was to combine two lenses, a plano-concave lens made of chemicals called 'flint glass' with a convex lens made of chemicals called 'crown glass'. This new arrangement of lenses could be combined in an 'achromatic' microscope that virtually eliminated the annoying aberrations and produced a reasonably clear and focused image.

This new instrument was quickly snapped up by the German scientists (mostly doctors) who were trying to dig down into the very fundamental substance of living things and trying to uncover the basic processes they felt were common to all living things. As this story tells, where ever they turned their microscopes, they found little 'sacks' (as Marcello Malpighi had called them in the late seventeenth century). Some scientists, like Schwann, were obsessive and looked at any and all possible living tissues. Although there were some differences, it began to look as if cells, what every their function, were universal and separate entities - like the building blocks of houses.

Science@a Distance
© 2002, Professor John Blamire