Page:Philosophical Transactions - Volume 029.djvu/439

 times ſeem to meet and joſtie ; and at other times to ſeparate, and fly one another. But this Motion was only Optical, and occaſioned by the Eye of the Spectator being carried away with the Earth in to the Eaſt; whilſt the exceeding rare Vapour of which thoſe Beams did conſiſt, being, as I take it, railed far above the Atmoſphere, was either wholly left behind, or elſe followed with but part of its Velocity, and therefore could not but ſeem to recede and move the contrary Way. And after the ſame manner as the Stars that go near the Zenith, paſs over thoſe Vertical Circles which border on the Meridian, much ſwifter than thoſe Stars which are more diſtant therefrom; ſo theſe luminous Rays would ſeem to recede faſter from Eaſt ro Weſt, as their Baſes were nearer the Eye of the Spectator; and è contra, flower as they were further off.

Nor are we to think it ſtrange, if after ſo great a Quantity of luminous Vapour had been carried up into the Ether out of the Pores of the Earth, the Cauſe of its Efferveſcence at length abating, or perhaps the Matter thereof conſumed; theſe Effluvia ſhould at length ſubſide, and form thoſe two bright Lamin which we have deſcribed, and whoſe Edges being turn’d to us were capable to emit ſo much Light that we might read by them. I chooſe to call them Lamin, becauſe, without doubt, though they were but thin, they ſpread Horizontally over a large Tract of the Earth Surface. And whilſt this luminous Matter dropt down from the upper Plate to the under, the many little white Columns were formed between them by its Deſcent, only viſible for the Moment of their Fall. Theſe by the Swiftneſs with which they vaniſhed and their great Number, ſhewing themſelves and diſappearing without any order, exhibited a very odd Appearence; thoſe on the Right ſeeming ſometimes to drive and puſh thoſe on the left, and vice verſa.