ALT 



gods were raised to a great height above 

 the {pound; those appointed for the ter- 

 restrial were almost on a level with the 

 surface of the earth ; and on the contra- 

 ry, they dug a hole for the altars of the 

 infernal gods. According to Servius, the 

 first were called alturia, the second ars, 

 and the last crobicult; but this distinction 

 is not t-v cry where observed, for we find 

 in the best authors, the wordara, as a ge- 

 neral word, including the altars of celes- 

 tial, infernal, and terrestrial gods. 



Hefore temples were in use, altars were 

 erected sometimes in groves, sometimes 

 in the high ways, and sometimes on the 

 tops of mountains; and it was a custom 

 to engrave upon them the name, proper 

 ensign, or character of the deity to whom 

 they were consecrated. Thus, St. Paul 

 observed an altar at Athens, with an in- 

 scription To the unknown God. 



In the great temples of ancient Rome, 

 there were ordinarily three altars; the 

 first was placed in the sanctuary, at the f oo t 

 of the statue of the divinity, upon which 

 incense was burnt, and libations offered : 

 the second was before the gate of the 

 temple, and upon it they sacrificed the 

 victims: and the third was a portable al- 

 tar, upon which were placed the offer- 

 ings and the sacred vessels. 



llcsides these uses of the altars, the an- 

 cients swore upon them, and swore by 

 them, in making alliances, confirming 

 treaties of peace, and on other solemn 

 occasions. Altars also served as a place 

 of refuge and sanctuary to all those who 

 Hcd to them, whatever crime they had 

 committed. 



ALTAR is also used, among Christians, 

 for the communion-table. 



Al.TKHNATK, in heraldry, is said in 

 cespect of the situation of the quarters. 



Tims the first and fourth quarters, and 

 the second and third, are usually of the 

 same nature, and are called alternate 

 quart i 



ALTERNATION is used for the dif- 

 ferent ways which any number of quanti- 

 ties may be changed, or combined 



COM HIXAT1O3T. 



ALTHJEA, marsh-mallow, in botany, a 

 genus of plants, with a double calyx, the 

 exterior one being divided into nine seg- 

 ments; the fruit consists of numerous 

 capsules, each containing a singh 

 h belongs to the Monodelphia I'olyan- 

 dria class and order. There are nine spe- 

 cies. The A. officinalis is perennial, and 

 flowers from .Inly to September. It grows 

 plentifully in salt marches, and on the 

 banks of rivers and ditches, in many parts 



ALU 



of England, Holland, France, Italy, Sibe- 

 ria, &c. It has been in great request in 

 every country where medicine has been 

 regularly cultivated. All its parts abound 

 with a glutinous juice, with scarcely any 

 smell or peculiar tas'.e. 



ALTiMKTKY, denotes the art of mea- 

 suring altitudes or heights, bee MK.NSI- 



lULTION. 



ALTITUDE, in geometry, one of the 

 three dimensions of body ; being the 

 same w ith what is otherwise called height. 



Altitude of a figure is the distance of 

 its vertex from its base, or the length of 

 a perpendicular let fall from, the vertex 

 to the base. 



Thales is supposed to have been the 

 first person who applied the principles of 



geometry to the mensuration of altitude : 

 y means of the staff he measured the 

 height of the pyramids of Egypt, making 

 the altitude of the staff and pyramid pro- 

 portional to the length of the shadows. 



ALTITCUE, in optics, is the height of an 

 object above a line, drawn parallel to 

 the horizon from the e\e of the ob.server. 



ALTITUDE of the eye, in perspective, is 

 its perpendicular height above the geo- 

 metrical plane. 



ALTITUDE of a star, f^c. in astronomy, 

 is an arch of a vertical circle, intercepted 

 between the stars and the horizon. 



This altitude is eithertrue or apparent, 

 according as it is reckoned from the ra- 

 tional or sensible horizon, and the diffe- 

 rence between these is what is called by 

 astronomers the parallax of altitudt. 

 Near the horizon, this altitude is always 

 increased by means of refraction. 



AxTrnmv qf*the mercury, in the baro- 

 meter and thermometer, is marked bv de- 

 grees, or equal divisions, placed by the 

 side of the tube of those instruments. 

 The altitude of the mercury in the baro- 

 meter, in and about the metropolis, is 

 usually comprised between 28.4 and o0.6 

 inches : in the course of the last 

 years it has not varied from these limits 

 more than twice. During the same pe- 

 piod, the thermometer in the shade has 

 been rarely higher than 82 or 80, anil 

 this seldom more than three or four times 

 in a whole summer, nor often lower titan 

 about 8 or 10 below the freezing point. 

 This decree of cold is not commmi. 



\LTO-Ur.l.lK\0. See UKI.IKV... 



ALUM, in chemistry and the arts, is 



denominated the sulphate of alumina, 



though it is not merely a combination of 



alumina with the sulphuric acid. It pos- 



tlic following characters : 1. It has 



sh astringent tasK'. C. It is aolu: 



