Text 4 -- THE ELECTRON MICROSCOPE
Text 4
THE ELECTRON MICROSCOPE
A modern electron microscope is about seven feet high, and the cheapest costs over £ 3,000. At the top is a cathode firing off electrons at 60,000 volts. The beam passes through three magnetic «lenses», corresponding to those of the condenser, the objective, and the ocular in an ordinary microscope, and through the object to be photographed. The whole action takes place in a very high vacuum, for air scatters electrons as fog scatters light. Special controls keep the electron voltage and the current through the objective lens steady to one part in 50,000. The specimen is mounted, not on a glass slide, but a very thin film of cellulose.
The techniques has been used in industrial chemistry. Apply the beam to the smallest dot on a photographic film, which looks like a faint1 cloud under an ordinary microscope, and we see a complicated tangle2 like a snarl3 of string. This result is being used for the improvement of very fine plates such as are needed for astronomy and aerial photography. Other industrial chemists are studying thin films of metal, and others again the synthetic fibres such as nylon and vinyon which are replacing silk and rays, and the plastics which are being used in so many branches of industry.
This microscope has definitely proved that the molecular theory of chemistry is true, for large protein molecules have been photographed, and their size and shape found to be the same as had been determined by other direct methods.
Probably its most important applications will be in biology. Bacteria which are so small that the ordinary microscope cannot distinguish their parts, turn out to have quite a complicated structure. Viruses, agents of disease far too small to be visible with the light microscope, have been photographed and different kinds can be distinguished. So far as I know, no photographs have yet been taken to show the detailed structure of human cells, but this will doubtless be done soon if it has not been done already.
The importance of this new tool for research lies in the fact that we still know very little about the structure of things smaller than the smallest cells we can see which are alive, but larger than the largest chemical compounds we can make which are not alive. Certainly some of the larger molecules show a few properties which are generally found in living things, and the smallest organisms do not posses all the qualities which we generally associate with life. But there is a considerable gap, and there are still people who say it is unbridgeable.
The history of science, and especially our knowledge of evolution, should make us very cautious about saying that any distinctions such as that between living and dead matter are absolute. The electron microscope is already helping us to bridge this particular gap.
1947
Література
John B.C. Haldane. Reader of Popular Scientific Essays. - Изд-во«Наука», М., 1993. - 235 с.