The word “electricity” is derived from the Greek “elektron,” which was the name for amber, a mineralised resin of extinct pine-trees. It was well-known to the people of pre-historic times; later to the early Egyptians, and, at a still later date, we have recorded how Thales -the Greek philosopher, who lived about the close of [...]
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Another method of isolating certain stones is by the action of heat-rays. Remembering our lessons in physics we recall that just as light-rays may be refracted, absorbed, or reflected, according to the media through which they are caused to pass, so do heat-rays possess similar properties. Therefore, if heat-rays are projected through precious [...] The fixing of the specific gravity of a stone also determines its group position with regard to weight; its colour and other characteristics defining the actual stone. This is a safe and very common method of proving a stone, since its specific gravity does not vary more than a point or so in different [...] Hardness is perhaps one of the most important features in a stone, especially those of the “gem” series, for no matter how colour, lustre, general beauty and even rarity may entitle a stone to the designation “precious,” unless it possesses great hardness it cannot be used as a gem or jewel. Consequently, the hardness of [...] Color is one of the most wonderful effects in nature. It is an attribute of light and is not a part of the object which appears to be coloured; though all objects, by their chemical or physical composition, determine the number and variety of vibrations passed on or returned to the eye, thus fixing their [...] |
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