SUCCESSORS OF NEWTON IN ASTRONOMY 



again referred to in a later chapter, Halley's views, 

 representing the most advanced views of his age, are 

 of interest. 



" The theory of the air seemeth at present," he says, 

 "to be perfectly well understood, and the differing 

 densities thereof at all altitudes; 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 forty miles high the air is 

 rarer than at the surface of the earth at three thousand 

 times ; and that the utmost height of the atmosphere, 

 which reflects light in the Crepusculum, is not fully 

 forty - five miles, notwithstanding which 'tis still 

 manifest that some sort of vapors, and those in no 

 small quantity, arise nearly to that height. An in- 

 stance of this may be given in the great light the 

 society had an account of (vide Transact. Sep., 1676) 

 from Dr. Wallis, which was seen in very distant coun- 

 ties almost over all the south part of England. Of 

 which though the doctor could not get so particular a 

 relation as was requisite to determine the height there- 

 of, yet from the distant places it was seen in, it could 

 not but be very many miles high. 



" So likewise that meteor which was seen in 1708, on 

 the 3ist of July, between nine and ten o'clock at night, 

 was evidently between forty and fifty miles perpendicu- 

 larly high, and as near as I can gather, over Shereness 

 and the buoy on the Nore. For it was seen at London 

 moving horizontally from east by north to east by 

 south at least fifty degrees high, and at Redgrove, in 

 Suffolk, on the Yarmouth road, about twenty miles 

 from the east coast of England, and at least forty miles 



YOL. iii. a 7 



