atlas 
or wanting. The general form of the hone is annular; It 
revolves :il)"iit :i pivot liirnished hy the odontoid pi...-.-- 
of tin; axis, anil follows tin- rotatory movement* of the 
head npim the neck. It is commonly aukylosccl with tin- 
axis in CM000O. Baa anbj/totto. 
4. A bound collection of maps. The wonl was first 
used ill tliis sense liy Mereator in the sixteenth eentun, 
in iillusion to the Atlas of mythology, whose 111:111. 
senteil as bearing a globe on his shoulders, was given on 
the title-page of such works. 
Urnce 5. A volume of plates or table* illus- 
trative or explanatory of sonic subject. 6. 
A si/.c of writing- or drawing-paper, 'JO by TO or 
34 inches. 7. [NL.] In cnto(.,alargelaiiielli- 
eorn beetle of tin- f:nnil y !<<-<irttl>inil<r; the atlas 
beetle, I'liiilciixiniHi nilnx. about I! inches long, 
and of a brilliant nietnllii'-green color. 
atlas- (nt'las), ii. [= Sp. ntlns = <). nllnxs = 
S\v. iitlii* = Dan. iitlux, ntliixl;, satin, < Hind. 
iillux, < Ar. ntlux, satin, < iitln.i, smooth, bare, 
blank, < tnliixii, make smooth, delete.] A kind 
of satin : a word formerly used in the Levant 
and in India. 
atlas-folio (at'las-fo'lio), n. [<otfal, 6, + 
fiilin.] A litrge square folio size of books. 
atlo-axoid (at 16-ak'soid), a. In anat., of or 
pertaining to the atlas and axis, the first and 
second cervical vertebne. Atlo-axoid ligament, 
one of three ligaments, anterior, lateral, anil posterior, 
connected with both the axis and the atlas. 
atloid (at'loid), . [<riM*l, 3, + -aid.] In mini., 
of or pertaining to the atlas; atlantal: usually 
as the second element of a compound: as, 
orri/iito-itttiHil ligaments. 
atmidometer (at-mi-dom'e-ter), n. [< Gr. a 
(aTfit6-), vapor (< ar/iAf, steam, vapor) 
a measure.] An instrument invented by Bab- 
ington for measuring the evaporation from wa- 
ter, ice, or snow. E. H. Knight. See atmom- 
etcr. 
atmo-. [< Gr. or/idf, vapor, steam (= Skt. dtiiirin, 
breath, = AS. ivtlim = OS. at horn = OFries. eth- 
ma= D. adem = OHG. dilum, dtum, MHG. atem, 
uti'ii, G. atem, athem, orient, also (prop, dial.) 
oden, breath), perhaps from the root repr. by 
Skt. -\/ vd, Or. af/vai (y * F a), blow, and so related 
to a^i>, air, aa6/ia, asthma, etc., and to E. wind 2 : 
see air 1 , axilinin, and wind 2 .] The first element, 
meaning vapor, in some compound words of 
Greek origin. 
atmqlogical (at-mo-loj'i-kal), a. [< atmology 
+ -ic-al.] Pertaining to atmology. 
A classification of clouds can then only be consistent 
and intelligible when it rests on their atmvlomcal condi- 
tions. Whcmll, Hist. Induct. Sciences, x. 2. 
atmologist (at-mol'o-jist), n. [< atmology + 
-('<.] One skilled in atmology; a student of 
atmology. 
The atmoloriutH of the last century. 
Wheimll, Nov. Org. Renovatum, III. ix. S 8. 
atmology (at-mol'o-ji), n. [< Gr. ar/idc, steam, 
vapor, + -Xoy/a, < ye>. speak: see -ology."] 
That branch of science which treats of the laws 
and phenomena of aqueous vapor. 
The relations of heat and moisture give rise to another 
extensive collection of laws and principles, which I shall 
treat of in connection with themistics, and shall term "'- 
molmi'i. Whetvell, Hist. Induct. Sciences, x., Int. 
atmolysation, etc. See atmolysation, etc. 
atmolysis (at-mol'i-sis), w. [< Gr. ar/jfa, vapor, 
+ Ai'-oif, a loosing, < \vecv, loose.] A method of 
separating mixed gases or vapors of unequal 
diffusibility by confining the mixture in a ves- 
sel of porous material, such as graphite, placed 
in a vacuum. See atmolyser. This method was first 
made known in 1863 by its discoverer, Professor T. Gra- 
ham, master of the English mint. 
atmolyzation (afmo-li-za'shon), . The sepa- 
ration of mixed gases by atmolysis. Also at- 
368 
atmosphere (at'mos-fer), . [= F. atmosphere 
= I'g. lllll/nxjilnTll = Sp. llliiiiixl'i fit = It. illlllil- 
xj'i ni = S\v. alninxfi r = I >an. iitinimfii-ri- = ( i. nt- 
iiinx/iliiiri; < XI,. iiliiiiixjilni-rii, < <lr. ti-u-, vapor. 
+ mjxujia, sphere: see sphere.] 1. The aeriform 
fluid which Hiirrounds the earth, and extends to 
tin undetermined height above its surface; tin- 
air. It is a mechanical mixtiM g robtm "I 
nitrogen and ^1 of oxygen, with a trace of carlion dioxid 
at 1. 1 a \ai ial.lc nuiintity of aqueous vapor, ammonia, o/.,ne. 
anil organic matter. 1 he comjiosition of the normal at mo 
sphere \niics hut slightly in din.-i.-nt lo.-aliti.-s. :dthotigh 
near tow ns it usual 1} < "n tains impurities, sneli as snljihil- 
fie :ieid, hyrlrochloric a.-id, etc. The movements of the 
atmosphere Constitute till- Wltl.K .Mid III it ;0<- tolllle'l n] 
produced clouds, mill, and .-now. Its density is gn-ate-t 
at the earth's surface, and decreases as the height al.ov.- 
thr earth ilHT.'a-e-v The atmosphere, like nther hodi.-s, 
gravitates toward the earth, and then-ton- has weight and 
exerts pressure. Its average weight at the level of the 
sea is alum! l.'i pounds ( 1 1.7) t" the square inch. 
2. A conventional unit of atmospheric pressure. 
Au at ni. .sphere is in English use the pressure of a vertical 
column of :(o inches of mercury at the freezing point 
at London ; in French use it Is the pressure of 701 milli- 
meters of mercnn -at the free/.in^ jHiint at Paris. For the 
absolute atmosphere in the ('. (i. >. (centimeter-gram- 
-i i ond) system, see altmjlutf. 'I he weight of the atmo- 
sphere to the s.jiiar.- inch is commonly enip! 
venient unit for pressures arising from other causes, such 
a* the weight of liquids, the for. . ot -!. am, . t< . : thus, a 
pressure ill a steam-boiler of n atmospheres means a pres- 
sure equal to t.'. pounds per square inch. 
I Ii. apparatus . . . was of great simplicity, allot glass, 
capable of resisting the pressure of many atiiujxphereit. 
Science, VIII. 66. 
3. The gaseous envelop surrounding any of 
the heavenly bodies. 
Ko sound, either loud or soft, could be heard by any 
inhabitant of the moon, Itecause the moon practically has 
no atmosphere. J. X. Lockyer, Spect. Anal., p. 22. 
4. Any gaseous medium: as, " an atmosphere of 
cold oxygen," Miller. 
For an atmotphere of any gas at uniform temperature, 
the height at which the density would be halved is the 
height of the homogeneous atmosphere for that gas, mul- 
tiplied by .69315; the gas is assumed to obey Boyle's law. 
J. D. Everett, Unit* and Phys. Const., p. 41. 
5f. An assumed outer envelop of force, efflu- 
via, etc., surrounding a body : as, an electrical 
tihiiox/i/icre. 6. Figuratively, intellectual or 
moral environment ; pervading influence. 
By the hearth the children sit 
Cold in that atmosphere of Death. 
Tennyson, In Meinoriam, xx. 
Absolute atmosphere. See absolute. Electric at- 
mosphere. See electric aura, under aural. 
atmospheric (at-mps-fer'ik), a. [< atmosphere 
+ -ic. Cf . spherical.'] 1. Pertaining to, existing 
in, or consisting of the atmosphere: as, atmo- 
spheric air or vapors. 
Quarantine cannot keep out an atmospheric disease. 
Coleridge, Table-Talk. 
2. Dependent on the atmosphere. 
I am an atmospheric creature. Pope. 
3. Caused, produced, or operated on by the 
atmosphere: as, rust is an atmospheric effect. 
Atmospheric Churn, a churn of various forms, in which 
atmospheric air is driven into the milk in order to agitate 
it, and also in order to obtain the specific effect of the air 
upon the milk in aggregating the oleaginous globules. 
Atmospheric currents. See current. Atmospheric 
engine, a variety of steam-engine in which the steam is 
admitted only to the under side of the piston and for the 
. 
atmblyze (at'mo-liz), v. t.; pret. and pp. at- 
molysed, ppr. atiiiolyzing. [< atmolysis. Cf. an- 
alyse, < analysis."] To separate, as gases or va- 
pors, by atmolysis. Also atmolyse. 
atmolyzer (at'mo-li-zer), . An instrument for 
separating gases. It consists of a porous pipe sur- 
rounded by an air-tighf cylinder connected with an aspi- 
rator, the lighter gases passing through the pores of the 
pipe, the heavier remaining in it. Also atmolyser. 
atmometer (at-mom'e-ter), n. [< Gr. arjuof, 
vapor, + ftcTpav, a measure.] An instrument, 
invented by Sir John Leslie, for measuring the 
amount of evaporation from a humid surface 
in a given time ; an evaporometer. It consists of 
a thin hollow ball of porous earthenware, to which is joined 
;i ^radtiated glass tube. The ball ami the tube are filled 
with water, the top of the tube is closed, and the instru- 
ment is exposed to the free action of the air. As the 
water transudes through the porous substance, and is 
removed in the form of vapor by the air, the extent of 
evaporation is shown by the sinking of the water in the 
graduated tube. 
Newcomen's Atmospheric Steam-engine. 
A, A, working-beam ; B, boiler from which steam Is admitted 
through the steam-cock, c, to the cylinder C ; A, rod, serving to lift 
a small pump; i, injection-cock ; P, piston; S, blow-valve, or snifting- 
valve ; T, tank ; IV, weights. 
lip-stroke, the down-stroke being effected by the pres- 
sure of the atmosphere caused by the formation of a 
vacuum under the piston through the condensation of 
the steam. This engine, invented by Papin in 1695, was 
first made a practical success hy N'ewcomen, ami was 
subsequently greatly improved by Watt, through the ad- 
dition of a separate condenser and air-pump. Atmo- 
spheric governor, an apparatus for controlling the move- 
ments of machinery by the use of air under pressure. 
Atmospheric hammer. () A hammer driven by means 
of compressed air, as the steam-hammer is operated ny 
steam. See xteam-hainm^r. (b) A hammer in which an at- 
mospheric spring is employed. The hammer-head is con- 
atom 
nected by a rod with a pUton working in a cylinder to 
which air is admit ted at the center ..( its length. V feip 
lo, atitl^ motion i* ;:iven to the ejlili. 
of the air routined between its other end and the pist.,n 
a corresponding motion is yivcn to th>- piston h. . 
m-eted with it. Atmospheric line, (a) In dlwnm ol 
steam |, tq tin- pencil when the 
-t.arn is shut otf from the piston of th<- indicator, and 
thus under the pr< --me of th. an phen alone. The 
li.-i^ht ot the sl< aneline altove this -how- tl, 
lh.- steam, and the depth of the vacuum line l.elou .-hows 
the degree of condensation which is then taking piaee 
in the cmjih, -. ('u ft. I'ark lines in tlie si.hit -pcctrnni 
produced l,\ th<- al.-oi ptioii of part of the solar ladiation 
by the terrestrial at m. .sphere, s,-, ,-y.. .',",, 
In addition to the lines of Kntunhofcr, imlnhita!. 
longing to the sun, there an- mam other dark lines in the 
solar sp.-' tinni uhieh originate from the absorptive ac- 
tion of tie- t.rn-- trial atmosphere, and ate then foie called 
Illnn, ,,,'' l.inii,- HI-,), p. ]!,.;. 
Atmospheric pressure. BM stmotfktn. .'.Atmo- 
spheric pump, a pnmp in which the water is forced nt-. 
the >nr! i,.n j,jp.- !.> at -ph. 1 1- |,re>-nre.- Atmospheric 
railway, a railway so constructed that th. motive [...wet- 
is derived from tin- pressure of tin attno-pli' 
a piston working in a continuous iron tube of nnitonn 
ln>re laid from one place to another, the presMin 1,, in- 
created by exhausting the air from that end of the tnl..- 
towanl which it is desired that the piston should advance, 
or by forcing in air behind it, or by both methods at 
The system has not I., . n found suitable for the ON 
purposes of a railway, though it is successfully worked 
for the conveyance of letters, telegrams, and light pack- 
ages. See jut. inn',.- i/. : ..it'i,. under pfwunwMft At- 
mospheric spring, a spring formed b\ the elasticity of 
a confined body of air. Atmospheric stamp, a stamp 
operated in the same manner as an atmospheric hammer 
(which see, above). Atmospheric tides, diurnal oscilla- 
tions of the atmosphere, produced by the attractions of 
the sun and moon, like the tides of the ocean, and indi- 
cated by minute variations of pressure on the barometer. 
atmospherical (at-mos-fer'i-kal), a. Same as 
fifni'txphfric. 
atmospherically (at-mos-fer'i-kal-i), adv. As, 
or as regards, the atmosphere ; by atmospheric 
force or influence. 
atmostea, n. Plural of atmosteon. 
atmosteal (at-mos'te-al), a. [< atmosteon + 
-al.] Pertaining to an atmosteon ; pneumatic, 
as a bone. 
atmosteon (at-mos'te-on), .: pi. atmostea (-ii). 
[NL., < Gr. ar/tAf, air, + oareov, bone.] In 
ornith., an air-bone ; a scleroskeletal ossifica- 
tion of a membranous tube or canal conveying 
air into the interior of a bone of a bird. 
The siphon-like tube which conveys air from the outer 
ear-passage to the hollow of the mandible may ossify, 
. . . resulting in a neat tubular " air-hone " or atmoitevn. 
Co<, Key to N. A. Birds, p. 168. 
atocha-grass (a-to'cha-gras), n. [Sp. atocha, 
esparto-grass.] A name sometimes given to 
the esparto-grass, Stipa tenacissiina. 
atok (a-tok'), n. [Peruv.] The native name of 
a kind of skunk, of the genus Conepatus, found 
in Peru, originally described by Humboldt as 
Gulo quitensis. Also called zorra. 
atoll (a-tol' or at'ol), . [Formerly atollon ; the 
name of such islands in the Maldive group; 
prob. < Malayalam adal, closing, uniting 
(Yule).] A coral island, consisting of a strip 
or ring of coral surrounding a central lagoon. 
Such islands are very common in the Pacific ocean. They 
often present an exceedingly picturesque appearance, a 
comparatively narrow strip of coral rock thinly coated 
with soil, and covered with a vigorous growth of cocoa- 
nut-, pam lanus-. and breadfruit-trees, inclosing a large still 
sheet of water, usually of considerable depth, and often 
well supplied with fish. The circle of coral is sometimes 
complete, showing no apparent communication between 
the inclosed lagoon and the surrounding sea ; but generally 
it is interrupted, and presents one or more openings suita- 
ble for the passage of boat*. 
atollont, n. See atoll. 
atom (at'om), n. [Early mod. E. also atoms, 
attorn (ami as L. atomits, atonios, with pi. atomi, 
sometimes atomic, ~> E. sing, atomic, atomyl, q. 
v.),< ME. attome, atonic, < F. atome = Sp. dtomo 
= Pg. It. atomo = G. Dan. Sw. atom, < L. atomus, 
< Gr. &ro/2Of, an atom, prop, adj., indivisible, 
that cannot be cut, < a- priv. + To/j6f, verbal 
adj. otTtpveiv, rafieiv, cut : see tome.] 1. An ex- 
tremely minute particle of matter: a term used 
generally with certain philosophic or scientific 
limitations, (a) A hypothetical particle of matter so 
minute as to admit of no division ; an ultimate indivisible 
particle of matter. See atomic philosophy, under atomic. 
Xo atom* casually together huri'd 
Could e'er produce so beautiful a world. 
Drydm, Epistles, i. 31. 
('<) A particle of matter assumed not to be divided under 
the circumstances considered ; a molecule. 
An a<om means something which is not divided in cer- 
tain cases that we are considering. 
W. K. Cli/ord, Lectures, I. 186. 
(c) In chem. and phytic*, the unit of matter; the smallest 
mass of an element that exists in any molecule. The 
number of kinds of atoms is the same as the number of 
the elements. AU atoms of the same element have the 
same constant weight. They are for the most part com- 
bined with other atoms, either of the same or of a different 
kind, forming molecules, and are indivisible by chemical 
