KEY AND INDEX 



current which it is the function of the dynamo to develop. See 

 "The Mechanism of the Dynamo," Vol. VI, p. 173; also "Niagara 

 in Harness," Vol. VI, p. 190. 



Artificial Gems. See "Gems," in present glossary. 



Artificial Stone, or Concrete. A stone-like substance made by 

 mixing cement with sand and pebbles or broken stone. Cement 

 itself is a mixture of powdered burnt clay, and powdered 

 hydrates of lime. It was extensively used by the Romans, but 

 little used by their successors until toward the close of the 

 nineteenth century. Modern cements differ somewhat from the 

 ancient and from one another, but all have as a base a mixture 

 of argillaceous and calcareous minerals (clays and lime com- 

 pounds). See chapter on "Artificial Stone, or Cement," Vol. 

 IX, p. 182. 



Astrolabe. An obsolete instrument for measuring the apparent 

 angle between two visual (usually astronomical) bodies. The 

 astrolabe, introduced about the middle of the fifteenth century, 

 superseded the cross-staff as an aid to the navigator, and was 

 in due course supplanted by the sextant. See "The Development 

 of the Sextant," Vol. VII, p. 18. 



Astrology. The pseudo-science that purports to study the 

 stars and planets with the intent to forecast or interpret terres- 

 trial events. Astrology flourished in Egypt and Babylonia and 

 in the Western world throughout the Middle Ages. It num- 

 bered among its practitioners some astronomers of note, after 

 the revival of learning, even including Kepler, who, however, 

 was probably skeptical as to the validity of its claims. It grad- 

 ually fell into disrepute with the advance of scientific knowledge. 

 See "Two Pseudo-Sciences," Vol. II, p. 141. 



Astronomy. The science that deals with the sidereal and 

 planetary bodies. Observational astronomy reached a relatively 

 high development in Egypt and Babylonia and was cultivated 

 with great success by the Greeks of the Alexandrian epoch. 

 The Arabs were adept star-gazers. But modern astronomy 

 dates from Copernicus, Kepler, Galileo, and Tycho Brahe. The 

 vast generalization of Newton gave it fresh impetus. Herschel's 

 perfected telescope opened up new fields, with particular refer- 

 ence to nebulae and double stars. Spectroscopy and photography 

 in the nineteenth century still further widened the scope of the 

 science. See "Egyptian Astronomy," Vol. I, p. 33; "Babylonian 

 Astronomy," Vol. I, p. 61; for Greek Astronomy, Vol. I, p. 212; 

 "Ptolemy, the Last Great Astronomer of Antiquity," Vol. I, 



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