Little Atlas on the coast, and the Aati- Atlas south of the Great Atlas. The Great Atlas contains the highest summits of the en- tire svstem, as the .Tebel Ayashi (14,600 feet) and Tamjurt ( 14,.500 feet.) The Anti- Atlas is less elevated, and shorter than the main chain. The Little Atlas begins in about longi- tude 7° W., and finally joins the coast ridge of the Rif. In the Algerian Atlas only two chains are distinguished, separated by an ele- vated plateau interspersed with numerous saline marshes, called Shotts. The northern chain. Tell Atlas, or Little Atlas, is cut up by coast streams and deep valleys into several separate groups. Its highest summits are more than 7000 feet. The soutliern range, or Great Atlas, is very wide, and sends off juimerous spurs into the' Desert. It reaches in its highest peak, Shelia, an altitude of 7011 feet. In Tunis the Atlas system spreads out into a number of separate mountains of inferior altitude. The rooks composing the Atlas system_ comprise igneous and sedimentary rocks, which belong chiefly to the Archaean and Paleozoic periods. Jurassic, as well as more recent Tertiary forma- tions, are also much in evidence. Copper, iron, salt, and several kinds of beautiful marljle, occur in the Atlas. Some of the sunnnits are under snow for the larger part of the year, but even the higliest peaks are usually without a snow cover in summer. Consult: P. Schnell, L'Atlas marocain (Paris, 1898): T. Fischer, "Ueber meine Reise im marokkanischen Atlas," in Zeitschrift der Gessellschaft fur Erdkunde, Vol. XXVI. (Berlin, 18(10).
ATLAS (Gk. 'ArXas). According to Hesiod's
Theogony, one of the Titans, the son of lapetus
and Clymene, and brother of Menoetius, Prome-
theus, and Epimetheus. Ajiollodorus, however,
says he was a son of Asia, and Hyginus, a son of
.^ther and (ia;a. The Pleiades were daughters
of Atlas and Pleoine, the Hesperides of Atlas and
Hesperis: and countless noble houses in Greek
legend traced their origin to the union of a
daughter of Atlas with a god. Through all an-
tiquity. Atlas bears the heavens on his shoulders,
and this is early declared a punishment for reljel-
lion against Zeus, which story was later elabo-
rated until Atlas became the leader of the Titans
in their war against the gods. Atlas, as bearer
of the heavens, appears in early Greek art on
vases and reliefs in connection with Heracles's
search for the apples of the Hesperides. In
statuary, Atlas is first represented by the Per-
gamene school. The plural, Atlantes (q.v. ), is
applied in arcliitecture to male figures serving
as colunnis. In consequence of the ancient views,
which made the vault of heaven rest on solid
])illars or other supports, the name Atlas, origi-
nally mythological and cosmogonie, was intro-
duced into geography. Mercator, in the Six-
teenth Century, gave the name Atlas to a collec-
tion of maps, probably because the figure of Atlas
supporting the heavens had been given on the
title-pages of such works.
ATLAS POWDER. A high explosive, used
for driving tunnels, sinking shafts and wells, sub-
marine blasting, removing wrecks, clearing ice
gorges and the like. It consists of nitroglycerin,
in proportions varying according to its use, with
small quantities of sodium nitrate and mag-
nesium carbonate, with wood fibre as an absorb-
ent. Like other varieties of dynamite, when not
confined it will burn harmlessly; but when fired
by a blasting cap it explodes with enormous
force. It is put up in cartridges 6 and 8 inches
in length and from seven-eighths of an inch to
2 inches in diameter, containing from 20 per
cent, to 7.5 per cent, of nitro-glycerin, according
to the special use for which it is desired.
ATMOM'ETER, or Evaporometeb (Gk.
dTjuis, a/»ios, vapor -f liirpof, ntetron, measiiTe).
An instrument used to measure the amount of
evaporation in the open air from a surface of
water. It consists of a round dish supplied with
an inclined scale to give a magnified reading of
the differences in level caused by the evapora-
tion. This loss can also be obtained by weighing
the dish and water at the beginning and end of
the experiment, in the Piche evaporometer the
evaporation is measured by a vertical graduated
glass tube closed at the upper end and open be-
low. The tube is filled with water, and the open
end is covered with a paper disk held in place by
a metal clamp. The water flows down to the
paper, from which it evaporates, and the amount
of evaporation is mea.sured by taking the differ-
ence in readings on the scale. The paper surface
gives off about one-third more water in a given
time than an equal extent of surface of water in
an open dish. The first instrument of this kind
was constructed by Sir John Leslie, and em-
ployed a porous earthenware ball instead of the
paper. Vhen the wind is blowing 5 miles an
hour the evaporation is 2.2 times as great as in
a calm; at 10 miles, 3.8 times; 15 miles, 4.9
times; 20 miles, 5.7 times; 25 miles, 6.1 times;
.30 miles, 6.3 times. Atmometers and other
meteorological instruments will be found de-
scribed in Russell, Meteorology (New York,
1899), a popular treatise.
AT'MOSPHERE ( Gk. dTij.6^, atmos, vapor +
(r(paipa. sj)haii-a, sphere, globe). The name applied to the mixture of gases and vapors surrounding any climate or sun, but especially the envelope of our globe. Spectrum analysis tells us much about the constituent gases and vapors, and even the relative motion of these in the atmospheres of the earth, the sun, and the distant stars; we know in general that nearly all of the chemical elements that occur in those are also present either on our earth or in its own atmosphere. The principal constituents of the earth's atmosphere are oxygen and nitrogen, in the ratio of 21 to 79 respectively. The next most important constituent is aqueous vapor, the proportion of which varies from 5 per cent, to nothing, depending upon the temperature and location of the sample of air that is analyzed. The other gases that are most commonly found are carbonic acid gas, wliose proportion varies slightly, but may be considered as being on an average 0.04 per cent., and to this extent may be considered as a normal constituent; when this gas is in excess (as in many dwellings where the combustion of fuel or illuminating gas is not properly guarded, or when persons are gathered together without proper provision for ventilation it is to be considered as an undesirable impurity. Traces of ammonia, hydro-carbons, and possibly ozone, are frequently encountered. The most interesting recent additions to our knowledge have resulted from our ability to cool and condense the air into a liquid form. By the fractional distillation of this liquid air, Rayleigh, Ramsay,
