TECHNICAL INDEX AND GLOSSARY 



not "flow." See "The Experiments of Stephen Gray," Vol. II, 

 p. 262; "The Transmission of Power," Vol. VI, p. 194. 



Civilization. Name somewhat loosely applied to the most re- 

 cent stage of ethnical development, in contradistinction to 

 "savagery" and "barbarism." In the terminology of some ethnol- 

 ogists, the word "civilized" is reserved for peoples that have 

 acquired the art of writing. 



Clock. The modern apparatus bearing this name is usually 

 actuated either by weight and pulley, by pendulum, or by coiled 

 springs. The most familiar type, the pendulum clock, was in- 

 vented by Huyghens in 1656. The clypsedra, or water clock, was 

 the most usual time-measurer throughout antiquity. See "In- 

 struments of Precision in the Age of Newton," Vol. II, p. 256. 



Coal-tar Colors. Pigments of an almost infinite variety of 

 colors and shades of color produced from the distillation 

 products of coal-tar, the basal form of which is known as aniline. 

 The first commercially important aniline color was produced 

 by Perkin in 1856. In recent years, coal-tar colors have revolu- 

 tionized the indigo and alizarine industries. See "The Coal-tar 

 Colors," Vol. VIII, p. 311. 



Coherer. A very delicate instrument, in the original Marconi 

 system, consisting essentially of brass filings in a vacuum tube, 

 with the aid of which the Hertzian waves used in wireless 

 telegraphy are detected. Coherers were invented independently 

 by Prof. D. E. Hughes (1880) and Dr. Branly (1890-91). See 

 "Wireless Telegraphy," Vol. VIII, p. 52. 



Cohesion. The property in virtue of which bodies tend to 

 hold together. The precise nature of this inter-molecular force 

 is not clearly established; it may be identical with gravitation. 



Collodion-emulsion Process. A photographic process de- 

 pendent upon the use of sensitized emulsion, the basis of which 

 is collodion. The process was introduced by Bolton and Sayce 

 in 1864, and gave a new impetus to photography. Subsequently, 

 gelatine was very generally substituted for collodion in making 

 the emulsion. See "Photography in its Scientific Aspects," 

 Vol. VIII, p. 231. 



Color-photography. The attempt to reproduce the natural 

 colors photographically has enlisted the efforts of a large num- 

 ber of experimenters, but as yet has met with only partial suc- 

 cess, although very beautiful glass "positives" may now be made 

 with comparative ease by the Lumiere "autochrome" process. 

 See "Photographing in Natural Colors," Vol. VIII, p. 234. 



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