ATL
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ATM
The Atbenata were built in form of Amphitheatres ; and were alfo incompafs'd with Seats, which Sidonius calls Cunei. See Am- phitheatre.
The two moil celebrated Athenaea were that of Rome, and that at Lions ; the former of which, according to AureliusVtllor, was built by the Emperor Adrian.
The Word is Greek, and is derived from Athens, a learned Ci- ty, where many of theft Affemblies were held; or from the Creek Name of Pallas, 'Aim, Goddefs of Science; intimating that Atheneum was a Place confecrated to Pallas, or let a-part for the Exercifes over which lhe prefides.
ATHEROMA, in Medicine, a Kind of a Tumour or Swell- ing, ot a pappy Confidence, without pain, or difcolouring the Skin. See Tumor.
The Atheroma is contain'd in a Cyflis or membranous Bag; and does not give way when touched with the Finger, nor re- tains any dent after preffure.
The Atheroma is thus call'd from the Greek Unit, a Kind of Pap or Pulp which the Matter of this Tumour refembles.— It is near a-kin to the Meliceris and Steatoma; and cured like them. See Meliceris and Steatoma.
ATHLETA, in Antiquity, a Wreftler, or a (Irong courage- ous Pcrlon, who employs himfelf in Exercifes of the Body, as running, wreitling, and other the like Gymnic Sports, for which the Andenrs had eilablilhed Prizes. See Exercise and Gym- nastic. See alio Game, Circus, &e.
The Athlete lived in continual Abltinence from Pleafures, to render themlelves the more vigorous and robull. See Absti- nence.
The Word comes from the Greek atMns, of itiia, certo, fug- no, I contend, I light. See Combat, Gladiator, &c.
ATIA. See Odio and Atia.
ATLANTIS, or Atlantica, in Antiquity, an Bland fpoke of by Pl.ao and other Writers, under feme extraordinary Circum- ftances; and render'd famous by a Controverfy among the Mo- derns about it.
The moll diliina Account of this celebrated Place, is given us in Plate's Timaus, and Critias ; which amounts, in a few Words, to what follows.—" The Atlantis was a large Illand in rhe We- " item Ocean, firuate before, or oppofite to, the Straights of " Gibraltar. Out of this Illand there was an eafy Paflage into " fome others, which lay near a large Continent exceeding all « Europe and Afia. Neptune fettled in this Illand, which he di- " llnbuted among his ten Sons; to the youngefl: fell the extre- " mity of the Illand call'd Gadir, which in the Language of the " Country fignifies 'Ev^rim, Fertile, or abundant in Sheep. The P Defcendants of Neptune reigned here from Father to Son, for " a great Number of Generations, in the Order of Primoge- " niture. They alio poUeffed feveral other Iflands; and palling in- " to Europe and Africa, fubdued all Libya as far as Egypt, and all « Europe to Afia Minor. At length the Illand funk under Wa- " ter ; and for a long Time afterwards, the Sea thereabouts was " full of Flats and Shelves.
The learned Rudbeds, Profeffor in the Univerfity of Vpfal, in an exprefs Treadle intitled, Atlantica five Manheim, maintains, very ftrenuoully, that Plato's Atlantis is Sweden; and attributes to his Country, whatever the Antients have faid of their Atlan- tis, or Atlantic Ifiaud.—Atter the little Abridgment we have gi- ven of Plato's Account, the Reader will be furprized to find Sweden taken for the Atlantis; and accordingly tho' Rudbeck's Work be full of uncommon Erudition, the Author pafles for a Vilicnary in this Point.
Others will have America to be the Atlantis; and hence infer, that the new World was not unknown to the Antients : But what Pluto fays, does by no means quadrate thereto. — America fhould rather lecm to be the vaft Conrinent beyond the Atlantis, and the other Iflands mentioned by Plato.
Becman, in his Hifory of Iflands, Cap. 5. advances a much more probable Opinion than that of Rudbeck's.— The Atlantis, ac- cording to him, was a large Illand extended from the Canaries to the Azores; and thefe Iflands ate the Remains thereof not fwal- lowed up by the Sea.
The Atlantis took its Name from Atlas, Neptune's eldeft Son, who mccccded hi; Father in the Government thereof.
ATLANTIDES, among the Poets. See Vergili*.
ATLAS, in Architecture, is a Name given to thofe Figures, or Half-Figures of Men, fo much ufed inftead of Columns, or Pilallers; to fupport any Member of Architecture, as a Balcony, or the like. See Column, &c.
Thefe are otherwife call'd Telamones. See Telamon.
Atlas, in Anatomy, the Name of the firll Vertebra of the Neck, which fapports the Head. See Vertebra and Neck.
It is fo call'd in allufion to the celebrated Mountain Atlas, in Africa, which is fo high, that it feems to bear the Heavens ; and to the Fable, in which, Atlas, the King of this Country is faid to bear the Heavens on his Shoulders.'
H j/* llas n0 'P'")' Apophyfis; becaufe the Motions of the Head don't turn on this Vertebra, but on the fecond. As it is
h t t0 tU ™ abouc as ° :en as the Heati moves round, had there been any fpiny Apophyfes, it would have incommoded the Motion of the Mufcles in the Extenfion of the Head.— It is alio
of a finer and firmer Texture than the other Vertebra,; and it dif- fers further from them in that thofe receive at one End, andard received at the other, whereas this receives at borh Extremes - for two Eminences of the Occiput are infated within its two' upper Cavities, which makes its Articulation with the Head ; and at the fame time, two other Eminences of the fecond Vertebra! are received within its two lower Cavities, by means of which they are articulated together.
Atlas is alfo a Title given to Books of univerfal Geography, containing Maps of the known Parts of the World ; as if they were view'd from the Top of that celebrated Mountain, which the Antients efteemed the higher! in the World; or rather on
u? Unt ° f tbcir holdin g tl]c whole World like Atlas.
We have alfo Atlas's of particular Parts, Sea-Atlas's, &c
J. he hrlt Work under this Denomination was the Greet Atlas ot Blaevj.
ATMOSPHERE, Atmosph^ra, an Appendage of our Earth; conliftmg of a thin, fluid, elaiiic Subftance, call'd Air, lurrounding the Terraqueous Globe, to a confiderable Heighth. See Earth. to
By Atmofphere is ufually underilood the whole Mafs. or Affem- blageot ambient Ait: Though, among the more accurate Wri- ters, the Atmofphere is reitrain'd to that Part of the Air next the Earth, which receives Vapours and Exhalations; and is termina- ted by the Refraction of the Sun's Light. See Refraction
The further or higher Spaces, though perhaps not wholly de- itituteof Air, are iuppoied to be poflels'd by a finer Subltance call d JEther ; and are hence denominated the JEtherial Reeion, or Space. See Ather, Heaven, &c.
A late eminent Author conliders the Atmofphere as a large Cbymical Veflel, wherein the Matter of all the Kinds of fublu- nary Bodies is copioutly floating; and thus expofed to the con- tinual Action of that immenfe Furnace the Sun; whence innu- merable Operations, Sublimations, Separations, Compofirions, Digeflions, Fermentations, Putrefactions, &c. See Chymis-
TR.Y.
For the Nature, Conftitution, Properties, Ufes, Diverfties, &C. of the Atmosphere, fee the Article Air.
We have a lavge Apparatus of Inllruments, contrived for in- dicating and meafuring the State and Alterations of the Atmof- phere; as, Barometers, Thermometers, Hygrometers, Manometers, Anemometers, &c. lee each under its proper Article, Barome- tfr, Thermometer, Hygrometer, &c.
The Atmofphere iniinuates itfelf into all the Vacuities of Bo- dies ; and thus becomes the gteat Spring of mod of the Mutati- ons here below; as Generation, Corruption, Diflolution, &c. See Generation, Corruption, Dissolution, &c.
Tis one of the great Difcoveries of .the modern Philo- fophers, that the feveral Motions attributed by the Antients to a Puga-vacui, are really owing to the Preffure of the Atmofphere. See FuGA-r<jc», Pump, Pressure, &c.
Weight of the Atmosphere.
Organical Bodies are peculiarly aflefted by this Preffure: To this, Plants owe their Vegetation ; and Animals their Refpiration, Circulation, Nutrition, e'irc. See Plant, Animal, Vegeta- tation, Circulation, drc.
To this alio wc owe feveral confiderable Alterations in the animal Oeconomy, with regard to Health, Life, Dileale, &c. See Health, &c.
And hence, a Calculus of the prccife Quantity of this Preffure, becomes a Point worthy of Attention.
Our Bodies, then, are equally prefs'd on by the incumbent At- mofphere; and the Weight they fultain is equal to a Cylinder of
Mr, whofe Bafe is equal to the Superficies of our Bodies Now,
a Cylinder of Air of the Height of the Atmofphere, is equal to a Cylinder of Water of the fame Bafe, and 35 Foot high; or a Cylinder of Mercury, 29 Inches high; as appears from the Tor- ricellian Experiments; as alfo from the Height to wh.ch Water afcends in Pumps, Syphons, dec. See 1 orricellian. See alio Pump, Syphon, &c.
Hence it follows, that every Foot fquare of the Superficies of our Bodies, is prefled upon by a Weight of Air equal to 35 cu- bicalFeetof Water; and a cubical Foot of Water, being round, by Experiment to weigh 76 Pound Troy Weight, therefore the Compafs of a Foot fquare upon the Superficies of our Bodies, fuftains a quantity of Air equal to 2<S6'o Pound : For 76+35:=: 2(ifjo ; and ib many Foot fquare as the Superficies of our Body contains, fo many times 2660 Pound does that Body bear.
Hence, if the Superficies of a Man's Body, contain 15 Iquare Feet, which is pretty near the Truth, he will fullain a Weight equal to 39900 Pound, for atStSo-J-ij^oooo, which is above 13 Tun for the ordinary Load.
The Difference of the Weight of the Air which our Bodies fullain at one time more than at another, is alio very great.— The whole Weight of Air which prefles upon our Bo- dies when the Mercury is highelt in the Barometer, is equal to 39900 Pounds. Whence, the Difference between the greater! and the lead preffure of Air upon our Bodies, may be prov'd to be equal to 3982 Pounds.
