| Abstrakt: |
Where order in variety we see, and where, though all things differ, all agree. The development of the modern atomic theory of matter owes much to the more venerable science of crystallography. One of the major clues leading to the discovery of the periodic table was the recognition that the elements are divided into groups having a family likeness. This derived, in part, from the appearance of crystals containing the elements in question. Crystallography was established during a remarkably fruitful decade around the late 1660s. Studying the shapes of crystals of alum, which is potassium aluminium sulphate, and possibly comparing them with orderly piles of musket shot or cannon-balls, Robert Hooke concluded that a crystal must owe its regular shape to the systematic packing of minute spherical particles. A few years later, in 1669, Niels Steensen, also known by the name Nicolaus Steno, noticed that the angles between equivalent pairs of faces of quartz crystals are always the same. Subsequent studies revealed that the same is true of other crystals, even though their shapes are different from that of quartz. Around 1690, Christiaan Huygens succeeded in explaining the three-dimensional structure of crystals of Iceland spar, or calcite, on the basis of regular stacking of equal spheroids. These solid figures are generated by rotating an ellipse about one of its axes. The next significant advance came in 1781. [ABSTRACT FROM AUTHOR] |
