KEY AND INDEX 



was produced by Niepce in 1827; but the honor of bringing 

 photography to a practical stage of development belongs to 

 Daguerre, dating from January, 1839. See "Photography in its 

 Scientific Aspects," Vol. VIII, p. 220. 



Photogravure. A process of engraving, done partly by pho- 

 tography, and by mechanical and chemical action on copper 

 plates, from which prints can be made in a copper-plate press. 

 See "The Reproduction of Illustrations," Vol. VIII, p. 184; in 

 particular p. 217. 



Phrenology. A doctrine, advanced by Dr. Franz Joseph Gall, 

 which maintains that the external configurations of the skull 

 are indicative of certain mental characteristics. See "The New 

 Science of Experimental Psychology," Vol. IV, p. 247. 



Physical Diagnosis. A method of external examination, in- 

 troduced by Corvissart, the physician to Napoleon, whereby 

 diseased conditions are detected by certain mechanical methods 

 of examination, such as "chest-tapping," etc. See "Nineteenth 

 Century Medicine," Vol. IV, p. 199. 



Physics. The science that deals with matter and its properties 

 and with the transformations of energy. From this it will be 

 seen that its scope is very wide and far-reaching. See "Galileo 

 and the New Physics," Vol. II, p. 93; "Modern Theories of 

 Heat and Light," Vol. Ill, p. 206; "The Conservation of 

 Energy," Vol. Ill, p. 253; "The Ether and Ponderable Matter," 

 Vol. Ill, p. 283; "The Royal Institution and Low-temperature 

 Researches," Vol. V, p. 29; "Some Physical Laboratories and 

 Physical Problems," Vol. V, p. 73; "Some Unsolved Scientific 

 Problems," Vol. V, p. 203. Electricity (q.v.) is a department of 

 Physics, and nearly all the appliances of the mechanical world 

 fall within the scope of Applied Physics. See, for example, the 

 chapter "How Work is Done," Vol. VI, p. 29. 



Physiology. In a restricted sense it is applied to that de- 

 partment of inquiry which investigates the functions of living 

 organisms, such as the functions of the brain, liver, etc. In a 

 broader sense it covers the sum of all knowledge concerning 

 living organisms. See "Anatomy and Physiology in the 

 Eighteenth Century," Vol. IV, p. 73; and "Anatomy and 

 Physiology in the Nineteenth Century," Vol. IV, p. 102. 



Pigments. The name given to paints, or any preparations used 

 by painters and dyers. Also, the coloring matter found in the 

 tissues of most animals and plants. See "Paints, Dyes, and 

 Varnishes," Vol. VIII, p. 258. 



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