PHOTOGRAPHS. 141 



process of taking photographic pictures by the use of 

 paper luade sensitive with bichromate of potash. 



Chrys'otype (Gr. chrusos, gold, and tiqios, a siiietch). — A pro- 

 cess of taking pictures, by photography, on paper impreg- 

 nated with a neutral solution of chloride of gold. 



Daguer'reotype (^Baguerre, the inventor, and Gr. tiipos, a 

 sketch). — A process by which all images produced by 

 the camera-obscura are retained and fixed iu a few mo- 

 ments, by the action of light upon metallic surfaces coated 

 with a salt of silver. 



Fer'rotype (Lat. /crrmn, iron, and Gr. fitjyoa, a sketch). — A 

 picture on a plate of sheet-iron, first covered with a sur- 

 face of black Japan varnish, and afterwards immersed in 

 collodion, and later in the silver solution. 



Helioch.'romy (Gr. helios, the sun, and chrome, color). — The 

 process by which photographic pictures in their natural 

 colors are obtained. 



He'liotype (Gr. helios, the sun, and tupos, a sketch). — Any 

 process for obtaining pictures by the actinic power of 

 the sun's rays on a prepared surface, from which to print 

 in fotty inks. 



Hyalotype (Gr. hialos, glass, and tupos). — A photographic 

 picture taken on glass. 



I'vorytype, or Hellen'otype. — A picture in which two finished 

 photographs are used. One is taken very light, the 

 paper made translucent by varnish, tinted on the back, 

 and laid upon the stronger print, so that there is a combi- 

 nation of effects. 



Opal'Dtype. — A picture on milky glass. 



Photogeny (Gr. pAos, j^hotos, light, and gennao, I produce). 

 — Tiie art or the practice of producing pictures by the 

 action of light on prepared paper. 



Photozincography. — A method of copying ancient documents, 

 etc., recently invented. Paper, after having been washed 

 over with a solution of the bichromate of potash and gum, 

 and then dried, is placed under a collodion negative, which 

 is a reduced picture of the document, obtained by the 

 photographic process. After it has been exposed to the 

 light, its whole surface is coated over with lithographic 

 ink, and a stream of hot water is then poured upon it. 

 As that portion of the coating which was exposed to the 

 light is insoluble, while the other parts are easily washed 



