KEY AND INDEX 



Marine Galvanometer. An instrument consisting of a tiny 

 magnet and a reflector with which telegraphic messages are 

 magnified by reflected light. With this instrument, the inven- 

 tion of Lord Kelvin, very weak currents of electricity can be 

 utilized for signaling. See "Instrumental Aids," Vol. VIII, p. 45. 



Medicine. For the story of the development of the science of 

 medicine, from the earliest time until the present, see "Scientific 

 Knowledge of the Egyptian Physician," Vol. I, p. 49; "Babylon- 

 ian Medicine," Vol. I, p. 75; "Empedocles, Physician, Observer, 

 and Dreamer," Vol. I, p. 132; "Hippocrates and Greek Medicine," 

 Vol. I, p. 170; "Galen, the Last Great Alexandrian," Vol. I, 

 p 278; "Arabian Medicine," Vol. II, p. 21; "Byzantine, and 

 Thirteenth Century Medicine," Vol. II, p. 31; "From Paracelsus 

 to Harvey," Vol. II, p. 156; "Medicine in the Sixteenth and 

 Seventeenth Centuries," Vol. II, p. 181; "Eighteenth Century 

 Medicine," Vol. IV, p. 182; "Nineteenth Century Medicine," Vol. 

 IV, p. 200. Also see chapters on Anatomy and Physiology of the 

 eighteenth and nineteenth centuries. 



Mercury-vapor Light. An electric light, invented by Mr. Peter 

 Cooper Hewitt, in which mercury vapor enclosed in a glass tube 

 is made incandescent by the passage of an electric current. 

 This type of lamp produces eight times as much light as the 

 ordinary carbon filament lamp with the same amount of power. 

 See "The Mercury-vapor Light of Peter Cooper Hewitt," Vol. 

 VI, p. 236. 



Meteorites, or Shooting Stars. Mineral or metallic masses, of 

 extraterrestrial origin, which fall upon the earth, or are con- 

 sumed while passing through the atmosphere toward the earth. 

 See "The New Science of Meteorology," Vol. Ill, p. 168. 



Meteorology. The science which treats of the motions and 

 phenomena of the earth's atmosphere, the study of climate and 

 weather, their causes, changes, and effects. See "The New 

 Science of Meteorology," Vol. Ill, p. 168. 



Mezzotint. A method of engraving on copper or steel, the 

 surface of which has been uniformly roughened by an instru- 

 ment called a "cradle" or "rocker." For dark tones the surface 

 is left undisturbed, the lighter effects being produced by scraping 

 away the surface. See "Mezzotint," Vol. VIII, p. 196. 



Micrometer. An instrument, used in connection with the 

 microscope, for measuring lengths and angles. 



Microscope. An optical instrument for magnifying minute 

 objects. Invented in 1590 by the Dutch optician Jensen. Im- 



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