KEY AND INDEX 



Goniometer. An implement for measuring solid angles, or the 

 inclination of planes, particularly the angles formed by the faces 

 of crystals. 



Gravitation. The universal force of attraction acting between 

 all masses of matter in the universe; in virtue of which, as 

 demonstrated by Newton, the power of attraction between any 

 two bodies is directly as their combined mass and inversely as 

 the square of their distance. The nature of gravitation remains 

 a mystery despite various attempts to explain it. See "Newton 

 and the Law of Gravitation," Vol. II, p. 236. For Le Sage's 

 theory of, see "Physical Problems," Vol. V, p. 213. 



Gyrocar. Name given to Mr. Brennan's monorail vehicle, 

 which owes its stability to the action of gyroscopic wheels. See 

 "The Gyrocar," Vol. VII, p. 195. 



Gyroscope. A revolving body; for example, a top, a hoop, or 

 the earth itself. More technically, a wheel adjusted in gimbal 

 frames to illustrate the principles of gyroscopic action; in par- 

 ticular, the stability acquired by a rapidly revolving body. See 

 "Gyrocar," Vol. VII, p. 195, and "The Gyroscope and Ocean 

 Travel," Vol. VII, p. 217. 



Gyroscopic Action. See "Gyroscope" in the present index. 



Heat. A manifestation of energy believed to represent active 

 molecular vibration. These vibrations may set up undulations 

 in the ether, which are interpreted as radiant heat; these undu- 

 lations can in turn transmit motion (i.e., "heat") to the molecules 

 of matter upon which they infringe as we see illustrated when 

 anything is warmed by the sun's rays. Heat was long supposed 

 to be an "imponderable" fluid. The true theory of heat was 

 developed by Count Rumford, Carnot, Mayer, Joule, and Helm- 

 holtz. See "Modern Theories of Heat and Light," Vol. Ill, p. 206. 



Heliocentric Theory. The true theory that the sun is the 

 central body of the planetary system was advocated in antiquity 

 by Aristarchus; but did not gain currency until put forward by 

 Copernicus in the fifteenth century. See "The New Cosmology 

 Copernicus to Kepler and Galileo," Vol. II, p. 52. 



Hertzian Waves. The electro-magnetic waves in the ether 

 that are utilized in wireless telegraphy. Named for Hertz, whose 

 studies first clearly demonstrated the characteristics of these 

 high-frequency ethereal waves. See Vol. Ill, p. 247; also "Wire- 

 less Telegraphy," Vol. VIII, p. 47, and "The Wireless Tele- 

 phone," Vol. VIII, p. 88. 



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