Page:Philosophical Transactions - Volume 029.djvu/441

 with a leſſer Globe included, in order to make that inner Globe capable of being inhabited, there might not improbably be contained ſome luminous Medium between the Balls, ſo as to make a perpetual Day below. That very great Tracts of the Etherial Space are occupied by ſuch a ſhining Medium is evident from the Inſtances given in the firſt Paper of this Tranſaction: And if fuch a Medium ſhould be thus incloſed within us; what ſhould hinder but we may be allowed to ſuppoſe that ſome parts of this lucid Subſtance may, on very rare and extraordinary Occaſions, tranſude through and penetrate the Cortex of our Earth, and being got looſe may afford the Matter whereof this our Meteor conſiſts. This ſeems favoured by one conſiderable Circumſtance, viz. that the Earth, becauſe of its diurnal Rotation, being neceſſarily of the Figure of a Flat Spheroid, the thickneſs of the Cortex, in the Polar Parts of the Globe, is conſiderably leſs than towards the Equator; and therefore more likely to give Paſſiage to theſe Vapours; whence a reaſon may be given why theſe Lights are always ſeen in the North. But I deſire to lay no more ſtreſs upon this Conceit than it will bear.

It having been noted that in the Years 1575 and 1580, wherein this Appearance was frequent, that it was ſeen not far from the Times of the two Equinoxes; it may be worth while for the Curious, to beſtow ſome Attention on the Heavens in the Months of September and October next; and in caſe it ſhould again happen, to endeavour to obſerve, by the Method I have here laid down, what may determine, with ſome degree of Exactneſs, the Diſtance and Height thereof; without which we can ſcarce come to any juſt Concluſion.