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554 CHRIST'S HOSPITAL CHROMIUM lord mayor. The course of study was gradu- ally augmented, until at present it embraces all the branches of a sound elementary educa- tion. The main establishment at London has four classical masters, two writing masters, two ushers, and mathematical, drawing, and singing masters, with about 800 scholars. In 1683 a branch hospital for preparatory train- ing was established at Hertford, which now has a classical master, a writing master, two ushers, two female teachers for the girls' de- partment, 400 boys, and 70 girls. The domestic economy of the hospital is on a plain but com- fortable scale, from which, however, many of the peculiarities of old times have but recently disappeared. Formerly the scholars perform- ed all the menial duties of the establishment, but now they are required merely to make their own beds. Until 1824 the boys break- fasted on bread and beer, and till more recent- ly ate from wooden trenchers and drew their beer from leathern blackjacks. Every Easter they visited the exchange and the lord mayor. Christ' s Hospital. The " king's boys " were formerly presented at court once a year ; and even now from Quinquagesima Sunday to Good Friday the hospital is visited by the public to witness the " suppings in public." The government of the hospital is vested in the lord mayor and aldermen of London, and in contributors of 500. Governors exercise the right of pre- sentation to the hospital, and have also the patronage of some ecclesiastical benefices. The hospital has long since ceased to be a "char- ity," properly so called, most of the pupils now admitted being children of freemen of the city of London and of clergymen of the church of England. Children whose parents have an income of 300 a year cannot be lawfully ad- mitted. No pupil is admitted under the age of 7, nor can he remain after 15, mathematical and Greek scholars excepted. The total in- come is about 40,000, and the expenditures about the same. The buildings of the hospital were mostly destroyed by the great fire in 1666, but were rebuilt under the direction of Sir Christopher Wren. They were repaired and partially rebuilt in 1825-'9. Excepting the new hall, which is one of the ornaments of the city, the buildings are irregular, although not incon- venient. Portraits of many historical person- ages, patrons of the institution, are preserved in its apartments. Among the eminent men educated at Christ's hospital are Bishop Stil- lingfleet, Camden the historian, Richardson the novelist, Coleridge, Lamb, and Leigh Hunt. CHROMATICS, that branch of optics which treats of the mathematical relations of colors. White light may be compared to a full chord in music, containing all the notes in the octave, but the comparison must not be insisted on too closely. By refraction through a prism, the colors may be separated more or less perfectly. This separation of colors by refraction takes place in nature by means of rain drops, pro- ducing the parti-colored rainbow, or by means of minute snow crystals, producing halos. By experiment, refraction can be produced in a great variety of ways, and the different colors of white light can also be brought out by other means than refraction. The mean distance be- tween two waves in a ray of light is -0000225 of an inch; in violet-colored rays, '0000167; and in red rays, '0000266. To chromatics also belongs the discussion of the phenomena of polarization and double refraction. These phe- nomena depend upon the form of the wave of light, and the direction of the motion in that wave, the wave itself always going in a straight line. It is in these most minute and subtle op- tical investigations that the undulatory theory of light has proved most fruitful. CHROMIUM (Gr. ^pa^ia, color), a metal so named from its tendency to impart beautiful colors to its compounds. About the year 1760 S. Lehmann, a Saxon mineralogist, was puzzled by a red mineral that was thought to contain gypsum, iron, and lead, and which was called red-lead spar. He wrote about it to Buffon in Latin, De nova Minerals Plumbi Specie Crys- 1 11 in <t rubra ; but no one could tell him what it was. Each successive chemist who exam- ined it detected something new, and the ore was in a fair way of contributing a complete mineralogical cabinet in itself, until Klaproth announced that it contained a new metal, and Vauquelin discovered in it a new acid. As soon as these two discoveries were announced, many of the chemists of the day attacked the mineral ; and it was not long before they found that it was composed of chromate of lead. Here the history of this element would have come to an end, if some years later an iron ore had not been discovered in France which also contained it, and thus afforded it in sufficient quantity for the various uses to which it was destined to be applied. Chromium ore has since been found in many localities, among others in the United States near Baltimore, where it is a source of profit to the owners of the mines. Deville obtained chromium in the fused state by igniting a mixture of chromic