316 PRESSURE IN THE AIR, 



lation as precise as possible, it is said, that as 

 the weight of air is to that of mercury, as 1 is 

 to 10-800, it must, of course, follow, that if 

 the weight of the atmosphere, be sufficient to 

 raise a column of mercury to the height of 

 30 inches, the whole atmospheric colum~ 

 must be 10-800 greater in weight; and, 

 consequently, that the whole extent of the 

 atmosphere, from the bottom to the top, can- 

 not exceed five miles one quarter. After 

 the proofs which I have advanced, in order to 

 show that the elevation of the mercury in the 

 tube, does not proceed from the pressure of 

 weight, I shall merely observe, that these limits 

 were proved to be false, by the facts which the 

 authors themselves produced ; they were pro- 

 ved to be false by the frequent appearances of 

 meteors, of those bodies which cannot exist 

 without the existence of air, at the elevation of 

 80 miles from the surface of the earth. In the 

 month of March, 1719, a meteor was seen, by 

 Dr.HALLEY,at the computed height of 73 miles, 

 whose diameter was 2,800 yards, or upwards 

 of a mile and a half; and whose velocity 

 amounted to 350 miles in one minute. In lat- 

 ter times meteors of a similar nature have been 

 observed, whose magnitude and motion, as well 

 as distance from the earth, was far more consi- 

 derable. The 18th of August, 1783, one of 

 these was discovered, whose distance from the 



