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Underground Paris: Mines generally have entries on the horizontal, many times from an outside quarry Floor and many workings continue on underground at that level. Some mines are inclined to follow a dipping stratum of rock. Surface quarries and underground mining are sometimes worked at the same location, winning high-grade stone from underground for special markets, while quarrying lower chemical-grade stone for use as aggregates.Nadar was a ceaseless, energetic worker. While still taking portraits he continued to illustrate books and to write novels. He constantly experimented. He was among the first to photograph by electric light, and produced a documentation of underground Paris, its catacombs and its sewers. He was the first to photograph from a balloon, in 1858.
Underground water reservoirs are of immense importance, particularly in the widespread arid regions of the world. In assessing the value of these reservoirs it is important to know how rapidly they are replenished, or, stated in a different way, one would like to know the "age" of underground water. The hydrogen of water coming from the atmosphere has a small content of tritium formed naturally from cosmic-ray reactions. Since tritium has a 12-year half life, it will have decayed from a static reservoir but will have a higher content in one which is continuously being replenished by rainfall, perhaps through underground streams from some distant source. |
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