VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 389 



This dipping and rising in the course of a meteor, is not more extraordinary 

 than its lateral deviation from a straight line. 



In regard to the velocity, it seems almost incredible ; as we have ufficient 

 data for computing it at the rate of 30 miles in a second. But if we allow that it 

 only moved through half the space in that time, we shall find the progression 

 of this body to have been above 100 times swifter than the mean celerity of 

 a cannon ball, and nearly equal to that of the earth in its orbit round the sun. 



As to its real size, we cannot pretend to determine that point with any pre- 

 cision ; since its dazzling brightness would occasion some deception, and the ap- 

 parent magnitude has been so differently represented by the observers. If the 

 meteor, when nearest to Dublin, appeared to Mr. Garret equal to the full moon, 

 then we shall find that its true diameter was about 2 miles , and if the farmer 

 at Ancram saw this body while it was vertical at Cambridge, of a size equal to 

 the crown of his cap, or to about half that of the full moon, we cannot allow 

 less than a mile for the real axis. On estimating from the observations made at 

 St. Andrew's and Dunfermline, the diameter was at least half a mile, and per- 

 haps much greater. However, as the imagination is so apt to enlarge such 

 objects, we shall fix the size of the globe at the smallest, and reckon it only 

 about a mile and a half round. 



The body must have been of a considerable bulk to have yielded such a light, 

 as that, when in the zenith of Cambridge, the farmer at Ancram, at the dis- 

 tance of above iGo miles, should, on entering his threshold, see the whole side 

 of his house illuminated by it ; and, to use his own expression, with a bright- 

 ness as of sunshine. And indeed the greatness of the light is every where taken 

 notice of, even at those places where the atmosphere was so thick as to hide 

 the tail, nay, the whole meteor, as at Auchenleck, where it was nearly 

 vertical. 



As for the tail, it was a stream of light several miles in length-; for this was 

 no deception, like what we suppose the train of a shooting star to be, but was 

 either a real flame, or, what is more probable, it consisted partly of flame, but 

 mostly of smaller masses of fire (which the observers call sparks, when falling out 

 of the lucid tract,) and of vapours or fuliginous particles, not heated red hot, but 

 illuminated by the parts actually burning. Perhaps these vapours were the chief 

 part of the composition, and which will account for its light being so much 

 fainter than that of the head ; since in some places where the air was less clear, 

 or the distance greater, we find the whole meteor described either as a round ball, " 

 or a spheroid (with the largest axis in the direction of its motion,) but without 

 a tail. In this last case, viz. that of the oval form, it is probable that, besides 

 the head, the beginning of the tail was also visible, as consisting of flame, 

 and therefore brighter than the rest ; and that both together appeared oblong to 



