592 ENCKE ENCRINITE and the design is impressed into the soft tinted clay. The hollows thus formed are filled with a semi-fluid clay of a rich or deep color poured into them and over the whole surface of the tile. In 24 hours this has hecome hard enough to admit of the surplus clay heing removed, which is done by placing the tile, still in the box, upon a horizontal wheel, and as it re- volves applying a knife or scraper entirely across, so as to rest upon the edges of the box. The surface is thus cut down so as to expose the pattern and the ground. The defects are removed with a knife, and the edges after being square are rounded off with sand paper. The tiles are kept for a week in a warm room called the greenhouse, and the drying is com- pleted in another called the hothouse. They are then baked like other articles of pottery, except that double the ordinary time is given to the process, and the oven is left six days to cool before the tiles are taken out. They con- tract in baking from one eighth to one six- teenth of their dimensions. The process is sup- posed to be nearly the same as that employed in the middle ages in France and England in making pavements for churches, and also for the beautiful pottery called Henry II.'s ware, peculiar to France in the 16th century. The French apply the term encaustic to prepara- tions of wax used for covering furniture and floors, which are then polished by friction. ENCKE, Job ami Franz, a German astronomer, born in Hamburg, Sept. 23, 1791, died in Span- dau, Aug. 26, 1865. He studied under Gauss at the university of Gottingen, served in the Hanseatic legion against Napoleon in 1813-'14, and in 1815 entered the Prussian military ser- vice, but afterward accepted a situation in the observatory of Seeberg near Gotha. In 1825 he was appointed director of the royal observa- tory at Berlin. He wrote many valuable me- moirs on astronomical subjects, of which the most important are the treatises published in the Astronomische Nachrichten, at Berlin, in 1831 and 1832, upon the comet then called by the name of Pons, the astronomer of Mar- seilles, who discovered it in November, 1818, but now known as Encke's comet. After its discovery Encke diligently applied himself to the determination of its orbit. Making use of the methods of Gauss, as explained in his work Theoria Motus Corporum Calestium, of calcu- lating an orbit assumed to be elliptical, he showed that its period of recurrence must be about 3 years, and that it was probably the same comet observed by M6chain in 1786, by Caroline Herschel in 1795, and by Pons in 1805. He calculated the effects of the pertur- bations it would experience from the planetary bodies, especially from Jupiter, and predicted its return in 1822, though it would probably not be visible in Europe. On June 3 of that year it was discovered at the observatory of Sir Thomas Brisbane, governor of New South Wales. Encke predicted its return in 1825, and with each reappearance as predicted more elements were afforded for computing its ex- act orbit It appeared again Oct. 30, 1828, and he was able to fix its orbit as within that of Jupiter, its greatest distance from the sun being four times the earth's distance, and its least distance but one third that of the earth, and its period of revolution 3 '29 years. By comparison of the times of its earlier and later apparitions, Encke was afterward led to detect a gradual acceleration of its movement, amounting to about 2 hours on each revolu- tion. This secular acceleration, never before recognized in the movement of any other celes- tial body, Encke ascribed to a resisting medium, which sensibly affects a body of the extreme rarity of this comet, which is transparent to its centre, but has no perceptible effect upon the denser planetary bodies. Resistance shortens the time of the revolution by giving greater ef- fect to the attraction of the sun, which then draws the body more forcibly toward itself, lessening the major axis of the ellipse, and thus its orbit of revolution. In investigating the perturbing effects of the planets upon this comet, of Jupiter in its aphelion, and of Mercu- ry in its perihelion, Encke was led to suspect that the mass of the former had been greatly underrated (a fact afterward established by Prof. Airy) ; and in 1838 he proved that La- grange had ascribed nearly three times too great a bulk to Mercury. Encke's explanation of the cause of the acceleration is not univer- sally accepted, although the fact itself is not questioned. Bessel particularly opposed the explanation ; by the English astronomers it is more favorably received. Besides these inves- tigations, Encke improved the theory of Vesta, and published a new method of computing per- turbations, especially for orbits considerably el- liptical. The planet Neptune was discovered at his observatory by Galle, his assistant. From 1830 Encke annually published the Astrono- misches Jahrbuch, and from 1840 Astronomische Beobachtungen auf der Sternwarte zu Berlin. In 1845 he published dissertations De Formulis Dioptricis ; and in 1846 a treatise Ueber das VerJidltniss der Astronomic zu den anderen WissenscJiaften. In the autumn of 1863 he re- signed his office. EJVCRINITE (Gr. Kpivov, a lily), a fossil genus of the order of crinoids, of the class echino- derms. It appeared among the earliest forms of animal life, its remains being preserved in the rocks of the Silurian period. In succeed- ing formations, nearly to the lias, they are often so abundant that calcareous strata extending over many miles are in great part made up of them. As described by Miller in his work on the crinoids, the animals of this family are fur- nished " with a round, oval, or angular column composed of numerous articulating joints, sup- porting at its summit a series of plates or joints, which form a cup-like body containing the vis- cera, from whose upper rim proceed five artic- ulated arms, dividing into tentaculated fingers more or less numerous surrounding the aper-
