VOL. XXIX.] PHILOSOPHICAL TRANSACTIONS. QQ 



j4n Account of several extraordinary Meteors or Lights in the Sky. By Dr, 

 Edmund Halley, S. R. S,* N° 341, p. 159. 



The theory of the air seems now to be perfectly well understood^ and its 

 different densities at all altitudes, both by reason and experiment, are sufficiently 

 defined; for, supposing the same air to occupy spaces reciprocally proportional 

 to the quantity of the superior or incumbent air, I have elsewhere proved, that 

 at 40 miles high the air is rarer than at the surface of the earth about 3000 

 times ; and that the utmost height of the atmosphere, which reflects light in 

 the crepusculum, is not fully 45 miles. Notwithstanding which, it is still 

 manifest, that some sort of vapours, and those in no small quantity, rise nearly 

 to that height. An instance-f- of this may be given in the great light the society 

 had an account of (vide Trans. Sept. 1676) from Dr. Wallis, which was seen 

 in very distant counties almost over all the south part of England. Of which, 

 though the Doctor could not get so particular an account as was requisite to 

 determine its height, yet from the distant places it was seen in, it could not but 

 be a great many miles high. 



So likewise that meteor which was seen in 17O8, on the 31st of July, between 

 9 and 10 o'clock at night, was evidently between 40 and 50 miles perpendicu- 

 larly high, and as near as I can gather, over Sheerness and the Buoy on the 

 Nore. For it was seen at London moving horizontally from E. by N. to E. by 

 S. at least 50 degrees high, and at Redgrave in Suffolk, on the Yarmouth road, 

 about 20 miles from the east coast of England, and at least 40 miles to the 

 eastward of London, it appeared a little to the westwards of the south, suppose 

 S. by W. and was seen about 30 degrees high, sliding obliquely downwards. I 

 was shown in both places its situation, but could wish some person skilled in 

 astronomical matters had seen it, that we might pronounce concerning its 

 height with more certainty; yet, as it is, we may securely conclude, that it was 

 not many miles more westerly than Redgrave, which, as I said before, is above 

 40 miles more easterly than London. Suppose it therefore, where perpendi- 

 cular, to have been 35 miles east from London, and by the altitude it appeared 

 at in London, viz. at 50 degrees, its tangent will be 42 miles, for the height 

 of the meteor above the surface of the earth ; which also is rather of the least, 

 because the altitude of the place shown me, is rather more than 50 degrees; 



* This is the first notice we find in the Philos. Trans, of Dr. Halley being secretary to the 

 Royal Society. 



t Dr. Halley here takes it for granted that the appearance is some kind of vapours enkindled, though 

 he is at a loss to account for their great height and motion. These circumstances induced Dr. Wallis 

 to conjecture that they may be small comets. See vol. ii, p. 389, of these Abridgments. 



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