2. History of Crystals and X-rays

History of Crystals and X-ray


Figure 3. Goniometer Mounted for X-ray diffraction

Crystals have been admired for a long time for their symmetry but it was not until the 17th century that crystals were investigated scientifically. The first crystal structure that was discovered is in the 1600s which was the structure of snowflake, by Johannese Kepler. He inferred that the hexagonal symmetry of snowflake crystals was due to a regular packing of spherical water particles. In the mid-1600s, it was investigated experimentally by a Danish scientist Nicolas Steno that the angles between faces are same and has a same regulations in every exemplar of a particular type of crystal. Quantitative crystallography began with Carnangeot’s invention of the contact of the goniometer in 1780s. Goniometer is an instrument which can drudely measure the angles between the faces of a crystal. In the mid-1800s William Hallowes Miller came up with a unique label f three small integers. This Miller indices is still used today for identifying crystal faces.

Gonio Type-U

Figure 4. Goniometer

The first half of the 19th century was the period of development of exact sciences. Some great mathematicians, i.e. Euler, Gauss, laid the foundations for mathematical, quantitative of celestial, and other mechanics of elasticity and optics. Experiments that were held between the 1820s and the 1830s disclosed the relation of magnetism of electricity. Faraday developed the concept of electromagnetic field which was given in mathematical expression by Maxwell in the 1860s. Other physicists were initially uncertain of the nature of X-rays, but soon realized that they were waves of electromagnetic radiation. X-rays were discovered in 1895, when the studies of crystal symmetry were concluded. In 1905, the photon concept was introduced by Albert Einstein and was accepted in 1920s, when it was confirmed by X-ray scattering from electrons.


Figure 5. Wave of X-ray