ATM' 



detail to recite even the principal of tlieiti. Cf its indif- 

 pcnfible ncceffity_ to tiie exigence of anim:il and vegetable 

 life, inllances frequeiUly occur in the courfe of this work. 

 Animals and vegetables, in their immcnfc variety, and from 

 their ftate of eggs and feeds to their fulleft maturity, owe 

 the commencement and continuance of their being to the 

 atmofphere that fiirrounds them. How much it conduces 

 to the fertility of the earth, by means of the parts that 

 compofe it, and to the convenience and comfort of man- 

 kind, by furnifliii.g a fit rcpofitory for the vapours that 

 defcend in refrefhing (liowcrs, and for the winds that form 

 an intercourfe of fociety and commerce witli dillant nations, 

 and by affording thofe redeftions and refraftions of hght 

 which ;hcd luflre over furrounding objects, and which forni 

 pleafing tranfitions from darknefs to day, gnd from day to 

 nip-ht, by means of twilight, it is altogether needlefs to 

 fpecify. The fubjeft would afford fcope tor much declama- 

 tion ; and v.-e might derive from it arguments that would 

 imprefs a thoughtful mind with jull and honourable fenti- 

 ments of the creator. Kow necefTary it is to the various 

 operations cf arts and fcience, as well as to the common 

 purpofes of life, will amply appear under the fcveral articles 

 which it would be almofl fnperfluous to mention. See - 

 Air, and the ieveral articles to which we have already 

 referred. 



Atmosphere, Method of navl^al'ing in ihe. See Aero- 

 station. 



Atmosphere of the Sun, Moon, Planets, andComets. See 

 the feveral articles. 



Atmosphere of fol'id or conffienl Bodies, is a kind of 

 fphcre formed by the effluvia, or minute corpufcks emitted 

 from thenir Mr. Boyle endeavours to fliew that all bodies, 

 even the hardefl and mod coherent, as gems, &c. have their 

 atmofpheres. See Gem, ' 



Atmosphere, in EleBrtcity, denotes that medium which 

 was conceived to be difTiifed over the furface of eleArified 

 bodies, and to confift of effluvia iffuing from them : whereby 

 other bodies immerged in it become endued vnxh. an elec- 

 tricity contrar)' to that of the body to which the atmofphere 

 belongs. This^vas firft taken notice of at a very early period 

 in the hiftory of this fcience, by Otto Guericke, and after- 

 wards by the academicians del Cimer.to, who contrived to 

 render the electric atmofphere vifible, by means of fmoke 

 attraeled by, and uniting itfelf to a piece of amber, and 

 gently rifing from it, and vanifliing as the amber cooled. 

 But Dr. Franklin exhibited this electric atmofphere with 

 great advantage, by dropping rofin on hot iron plates held 

 under bodies eleftrified, iVora which the fmoke rofe and 

 encompatfed the bodies, giving thera a very beautiful ap- 

 pearance. He made other obfervations on thefe atmo- 

 fpheres ; he took notice that they and the air did not feem 

 to exclude one another ; that they were immoveably re- 

 tained by the bodies from which they iffued ; and that the- 

 fame body, in different circumilances of dilatation and con 

 traftion, is capable of receiving or retaininT more or lefs 

 of the ekelric fluid on its furface. However, the theory 

 of electrical atmofpheres was not fufRciently explained and 

 underftood for a co'nfiderable time; and the inveftigaticn 

 led to many very curious experiments and obfer\'ations. 

 Mr. Canton took the lead, and was followed by Dr. Frank- 

 lin ; Mefr. Wilcke and Epinus profecuted the inquiry, and 

 completed the difcovery. The experiments of the two 

 former gentlemen prepared the way for the conclufion 

 that was afterwards drawn from them by the latter, though 

 they -retained the common opinion of eledtric atmofpheres, 

 and endeavoured to explain the phenomena by it. ' The 

 conclufion was, that the eleAiic fluid, when there is a re- 



A T O 



dundanry of it in any body, rep^^ls the eledlric fluid in any 

 other body, when they are brought within the fphcre of 

 each other's influence, and drive.- it into the remote parts 

 of the body, or quite out of it, if there be any outlet for 

 that purpofe. 



By atmofphere, M. Epinus fays, no more is to be un* 

 derflood than the fphcre cf action belonging to any body, 

 or the neighbouring air eleitrified by it. Sig. Beccaria 

 concurs in the fame opinion, th.at electrified bodies have no 

 other atmofphere than the electricity communicated to the 

 neighbouring air, and which goes with the air, and not 

 with the eleftrified bodies. And Mr. Canton likewife, 

 having relinquiihed the opinion that eleftrical atmofpheres 

 were compo(x:d of efHuvia from excited or eleftrified bodies, 

 maintained that they only rcfult from an alteration in the 

 ftate of the eleftric fluid contained in, or belonging to the 

 air furrounding thefe bodies to a certain diftance; for in- 

 ft;t»ice, that excited glafs repels the eleftric fluid from it, 

 and confequently beyond that diflance makes it more denfe; 

 whereas excited wax attrafts the eleftric fluid exifling in 

 the air nearer to it, making it rarer than it was before. 

 In the courfe of experiments that were performed on this 

 occalion, Meff. Wilcke and Epinus fuccetded in charging 

 a plate of air, by fufpending large boards of wood covered 

 with tin, with the flat fides parallel to one another, and 

 at fome inches afunder ; for they found, that, upon eleftri- 

 fyiiig one of the boards pofitively, tire other was always 

 negative; and a fliock was produced by forming a com- 

 munication between the upper and lower plates. Beccaria 

 has largely confidered the fubjeft of eleftric atmofpheres, 

 in his Artificial Eleftiicity, p. 179, &c. Eng. edit. Dr. 

 FrieiUey's Kifl. of Eleftricity, vol. ii. feft. 5. Cavalto's 

 Eleftricity, vol.i. p. 241. vol. iii. p.282. SeeCoNDENSER, 

 and Conductor, Luminous; and Experiments in Electr,:- 

 city. 



Atmosphere, Magnetic, denotes the fpherc.within which 

 the virtue of the magnet, &c. afts. 



Atmospherical Logarithmic. See Logarithmic. 



ATNAH, or Carrier Indw.m, in Geography, a tribe of 

 Indians in the north-well continent of America, inhabiting 

 the banks of the Columbia river, fonth of the Nagailer 

 Indians, about N. lat. 52", and W. long. 122°. The 

 Atnah language, of which Mr. Mackenzie obtained fomc 

 fpecimens, has no affinity to any witli which he was ac- 

 quainted. Mackenzie's Journal of a Voyage through the 

 N. W. Continent of America, p. 258. 



ATO^'I, formed of the privative k, and -^.^vrx, I divide, 

 in Philofoplyy, a part or particle of matter, fo minute as to 

 be indivifible. 



Atoms arc properly the minima naliira, the laft or ulti- 

 mate particles into which bodies are divifible ; and are con- 

 ceived as the firfl; rudiments, or component parts of all phy- 

 flcal magnitude ; or the pre-exiftent and incorruptible mat- 

 ter whereof bodies were form.ed. 



The notion of atoms arifes hence, that matter is not divi- 

 fible in infinitum. And hence the Peripatetics are led to 

 deny the reality of atoms, together with that of mathema- 

 tical points : an atom, fay they, either has parts, or it has 

 none ; if it hath none, it is a mere mathematical point ; if 

 it hath, then do thefe parts alfo confift of others, and fo on 

 to infinity. 



But this is to recede from the genuine charafter of atoms, 

 which are not elleemed indivifible, becaufe of their want of 

 bignefs, or parts (for all pliyfical maj'nitude mnft have three 

 dimenfions, length, breadth, and thicknefs, and all extenfion 

 is divifible) ; but they are indivifible on account of their foli- 

 dity, hardnefs, and impenetrability, which preclude all divi-' 



Con 



