Page:Philosophical Transactions - Volume 029.djvu/437

 not very obvious, but demonſtrated from ''Prop. 5. Lib. I. Theodoſii Spharic''. For by it all Lines erect on the Surface paſs through the Center, where meeting with thoſe from the Eye, they form the Plains of Vertical Circles thereto. And by the Converſe hereof it is evident, that this luminous Matter aroſe nearly perpendicular to the Earth’s Surface, becauſe it appeared in this erect Poſition. And whereas in this Appearance (and perhaps in all others of the Kind) thoſe Beams which aroſe near the Eaſt and Weſt, as L, M, N, were furtheſt from the Perpendicular, on both ſides inclining towards the South, whilſt thoſe in the North were directly upright: the cauſe thereof may well be explained by the Obliquity of the Magnetical Curves, making ſtill obtuſer Angles with the Meridians of the Terrella, as they are further from its Poles.

Hence alſo it is manifeſt how that wonderful Corona that was ſeen to the Southwards of the Vertex, in the Beginning of the Night, and ſo very remarkable for it’s tremulous and vibrating Light, was produced; to wit, by the Concourſe of many of thoſe Beams arifing very high out of the circumjacent Regions, and meeting near the Zenith: the Effluvia whereof they conſiſted mixing and interfering one with another, and thereby occaſioning a much ſtronger but uncertain wavering Light. And ſince it is agreed by all our Accounts that this Corona was tinged with various Colours, ‘tis more than probable that theſe Vapours were carried up to ſuch a Height, as to emerge out of the Shadow of the Earth, and to be illuſtrated by the direct Beams of the Sun: whence it might come to paſs that this firſt Corona was ſeen coloured and much brighter than what appeared afterwards in ſome Places, Where the Sight thereof was more than once repeated, after the Sight was gone down much lower under the Horizon. Hence alſo it will be eaſily underftood that this Corona as net one and the ſame in all Places, but was