THE CENTURY BOOK OF FACTS. 



quartz or flint, and feldspar the kaolin and 

 quartz to give hardness, and the pipe-clay and 

 feldspar to yield a flux sufficient to bind the 

 masses firmly together. The materials are 

 ground into a fine powder and then mixed with 

 water in a machine called a " blunger," which 

 is a box containing paddles worked very 

 rapidly. When the matter has been thoroughly 

 mixed it is drawn off and forced by a hydraulic 

 pump through a series of sieves and then 

 worked up in what is called a pug-mill, after 

 which it is cut by a fine wire into rectangular 

 blocks. These blocks are then molded into 

 the shape of the article desired, some by the 

 use of a lathe, and some by simply shaping 

 them with the hands. The pieces are thus 

 partially dried, turned on a lathe with a sharp 

 tool to give them a uniform surface, dried 

 slowly in a drying room, then baked in an oven. 

 I'n baking the ware is kept at a white heat for 

 thirty-six hours. The pieces are then glazed 

 by being dipped in a mixture of ground feld- 

 spar, ground flint, sal soda, plastic clay, and 

 boracic acid, the whole pulverized and mixed 

 with a small proportion of white lead and a 

 little cobalt blue. This glaze is mixed with 

 water, the articles are dipped in it one by one, 

 receiving .a deposit like a thin paste on the 

 surface, which, when placed in the oven again, 

 fuses and flows over it, making a coating of 

 glassy smoothness. Fine, white china or 

 porcelain is of course made of finer material 

 than crockery, but the process of manufacture 

 is similar. 



Cryolite is a snow-white mineral, partially 

 transparent, of a vitreous luster and of brittle 

 texture. It is so named from its fusibility in 

 the flame of a candle. It is a compound of 

 sodium, fluorine, and aluminum, and is used 

 for the preparation of the metal aluminum. 

 It occurs in veins in gneiss with pyrites and 

 galena, and has been found in western Green- 

 land and at Miyask in the Ural Mountains. 

 It is extensively employed in the United States 

 in the manufacture of white porcelain glass, 

 and also in the preparation of caustic soda. 



Daguerreotype. The name given to a 

 process invented by M. Daguerre of Paris in 

 1839, by which perfect facsimiles of objects 

 are transferred upon thin copper plates, plated 

 with silver. Tim images are produced by the 

 action of light upon the iodine through the 

 focus of the camera obscura. An apparatus 

 somewhat kyidred in design was in contem- 

 plation about the same time by M. Niepce, 

 and about five years previously by Henry Fox 

 Talbot of London ; the original idea, however, 

 is traceable as far back as the days of Roger 

 Bacon. So important a discovery in the fine 

 arts was the daguerreotype deemed by the 



French government, that it awarded to its in- 

 ventor a life pension of 6,000 francs. 



Damascus Steel. The skill of the Dam- 

 ascenes in the manufacture of steel became 

 famous in Europe at the time of the Crusades, 

 but the secrets of their process have never been 

 revealed. A Russian mining engineer, Gen- 

 eral Anosoff, by analysis and examination, 

 however, succeeded in making steel that could 

 scarcely be distinguished from it in appear- 

 ance. The essential point of his process was 

 melting the iron in crucibles with graphite and 

 a small quantity of dolomite ; but the details 

 of working these materials with success were 

 of course known only by himself, and the 

 quality of the steel produced by the works 

 since his death has very much deteriorated. 

 An imitation of Damascus steel is also made in 

 America and is often known by that name, 

 though its proper appellation is damask steel, 

 so called from the peculiar damask figures on 

 its surface. 



Damask Linens and Silks. They 

 were first manufactured at Damascus, and 

 hence the name ; have been imitated by the 

 Dutch and Flemish. The manufacture was 

 introduced into England by artisans who fled 

 from the persecutions of Alva, 1571-3. 



Day and Night. -The earth has two con- 

 stant motions : (1 ) its daily motion, or rotation 

 on its axis (its snorter diameter), from west to 

 east; (2) its yearly motion, or movement in a 

 nearly circular path (called its orbit) around 

 the sun. The length of time the earth is turn- 

 ing on its axis is called a day. Every part of 

 the earth's surface being successively carried 

 into light and shade, the daily rotation causes 

 the phenomena of day and night. The length 

 of time the earth is in passing around the sun 

 is called a year. It turns on its own axis in 

 the same time about 365 times, hence there 

 are 36o|days in a year. As the earth revolves 

 from west to east, the sun will appear to 

 travel from east to west. At the equator the 

 days and nights are always twelve hours long ; 

 the farther a point lies from the equator, the 

 longer are its longest day and its longest night. 

 At the poles the year is made up of but one 

 day and one night, each lasting six months. 

 All places in about 66^ degrees of latitude, 

 north or south, have one day in the year 

 twenty-four hours long, and one night of an 

 equal length. 



Dew. For any assigned temperature of 

 the atmosphere there is a certain quantity of 

 aqueous vapor which it is capable of holding 

 in suspension at a given pressure. Converse! y. 

 for any assigned quantity of aqueous vapor 

 held in suspension in the atmosphere there is 

 a minimum temperature at which it can re- 



