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Show [M.P.] Convergence near our Zenith. ueries. 519 [f § 28. " --and thus form the "mum, as they are called, and 518 Are and parallel Rays qu‘lw Aurora. he thought each at their maximum ; but as they prevail moft when the elietts of the MM may be conceived uftlally molt complete, one fhoultl hence {uppofe the cold necefl‘ary for their formation was harder to procure, than flmple moiflure. .E.] { 3 § 2*. " The atmofphere of the polar regions being denfe, " and its moifiure frozen, will not any light therein appear to us as " a {cgment ofa circle, darkifh in colour, &C." I once thought that Dr. Franklin intended a diliinflion here between that/i'fI/rfl' {rig/Jr, {0 often fecn from theft: latitudes in the northern part of‘our horizon; as cppofcd to thol‘e mammal/g figured lights, which come to be delcribetl in the next paragraph under the head of raw: In this cafe the fettled light is only confidered as arifing from the illu- mination of the atriq/f/W'r‘, by otlm- rays, which are lefs elevated or farther northward, and tlteililel\=es not di inetly teen; the atmofpherc being fluted to be dents, as more reflecting and better retracting that light; and clear, a bettertranfmitting it, as well as the light of the liars beyond-But it‘Dr. Franklin is here defcrihing (which is molt probable) that dark part of the heavens fecn at the foot of the {alient points of the {evcral rays to the north; then perhaps the caufe is only owing to that part ofthe heavens below the rays, (that is, below the height \VllCt‘C the fluid begins to be luminous) being rendered dark by the contra/I with this light. Ifa tangent is drawn to the globe in our latitudes, and that tangent produced towards the north, the elevation of it with refpeé't to the polar air is very confiderablc; not however greater than that, which fome philofophers have at times, attributed to the auroras. But if the auroras lhould be held to originate at any time, or at leal‘t firll to 5mm]: cuff/v15, at any dil'tanee from the pole; the whole will ceafe to be a difficulty. 13.] " other figures mentioned in the hillories of this meteor."--~As to thofe lights which feem to have a center near our zenit/J, perhaps they are thus difpofed, in conleqtrence of the roving fluid (extended northward and fimthward, caftward and wellward, through the writ and general vacuum) bting now brought to a focus by aconduélor; thence to link into humid air below as into a quenching "* pit of darknel‘s; or (which is the cafe of Dr. Franklin's [row/z) to {ally forth again to tome new conductor aloft. But 1 mull here beg to introduce {ome queries. 1°. thy {hould our lililOi‘ics {peak or this mean of general centergence, as being ufirally to the jinn/Br. ‘dof our zenith here? ls it owing to local moiltnefs in the atmoiphere there, from {cas or wet land below; or to that being ufually the latitude, where the fluid in its progrefs firlt meets with humidity f frequent and Elevated enouflt to attract it? 1‘. ls it again from local incidents that the euro. are ul‘ually obferved at Upial in Sweden to appear to the weltward of north; and in Greenland and lrlutll'on's ay, to the enfl or leuthwnrd of cal}, but never to the mr/lnvard or north~eall1 ?-30. Is the alleged fact of the/i/jmz/Em pf they? (rp‘fif/umzt‘ci", for feveral ages, at differ ' periods in our latitudes; and the greatfrequeney of them {ortlte . so or 60 years putt; to be at all held connetted With the luppolrtioa; ol‘forne of our bed philofcphers, that there are accounts wlnen be.n‘ 1'»; f/rmc'r time: m the r; o R 'r H, ‘than 15 utual fpeal: ~u'rzrmir at. 'it diminut' ,of the ire, Sze. both asto its now; with :1 call won as anon-co doctor, Lien? Or are weto extent, and its pc‘ take oppotite lit; ' ' ions; and ' v thatthe'ezu‘th's gromngwarmur to penetrate higher up, yd ol‘lztte, in .illllC t arts, has inali , ? 4‘. lheabove 1 to Q ~ fitted in the tormation or the. air ‘ 'ttlztnd, being .11 latitude 05", and in l-luc : ‘ carol: 21:, path: that the aurora m‘igimr. ‘5 in tuole ' ‘ llav é't qt)‘, ' e ties : or does the fluid only 1'; d-L'Jl thither 1 orr hrr'tn ll ‘ ' " The rays ofeleélric matter diverge, I've."- Pilfll'tjul‘iif from the no th, remaining; in ilible till attended With Such rays undoubtedly may diverge from repellency, when they arrive in the enlarged degrees of longitude. They would alto by 5 . To den riniue this, ought not exocriuitnts to D: pure made in rat ietlair, both dry and vapnry, denfirr and rarer, [* § 28 and 24. the laws of optics, appear near together at their farther ends in the north, even though really parallel: Like the parallel rays of the fun; which appear near together towards the fun, wide over the fpeftalor's head, and converging again if they pats the {pettator and get to the cppofite parts ofthe horizon; (which left cafe Dr. Smith in his Optics, mentions to have feen; asl have indeed done myfelt', more than once.)-Pcrhaps however, the degree of'feparaticn of the rays in the aurora, depends much on the pofition of the attrafiing condué‘tors at their hither end: Though I haveobferved lights {hootiug alcng a remarkably (rooted track in the heavens, at diilant re- peated times, owing apparently to the pofition of a particular fat of s'utrrmdiate condué‘tors. E.) [§ 29. tay and impregnated, cold Itildliot: and ought we not to b * able to ".fii'rn; but when the fluid moi es naked in any quantity at; and when it enters a tn, it is as tar as we know, Is conduétor, its libht as tar ..s we know is dirctlly :‘xlm- {01ch into a nut-e is :omeracnm to 'th: {oath of the zenith is, by tome, in .l l'liilul'sphy, Vol.1. part 2. p. 164.7.) . ‘ north. the (Hugging from p. 479; Krintx's "grow: 0‘. Greenland, f‘mit': ‘rtl‘llicgl t77c, p. (3: r.- ‘ t". L :48Greenland let'm to at. . . rum about the 'c hurt r39 teen in Lllpldl ' I Fundy, U u u 4‘ quarter 01 it; and. Ll |