2,6 On the RESISTANCE of the AIR, 8cc. 



propofe alfo, at the fame time, to try the refiftance of fome other 

 figures. 



12. 3<#k> From any of the numbers in the fixth column, it 

 appears, that the altitude of a column of air, whofe prefTure is 

 equal to the refiftance on the round fide of the hemifphere, is 

 half the altitude due to the velocity of the figure ; that is, half 

 the altitude from which a body mufl freely fall by gravity to 

 acquire that velocity ; and, in this inftance, agreeing with the 

 theory. Thus, if we take the velocity of 10 feet per fecond, 

 whofe refiftance in the fixth column is 12.4, we fhall have* as 

 32 2 : io 2 :: i6:- 6 ° 4 -= 1.56 feet, which is the altitude due to 

 to the velocity 10, and the half altitude is .78 ; but the weight 

 is 12.4 ounces, which being divided by 51.14, to reduce it 

 from the axis to the centre of the body, gives .241 1 oz. for the 

 true refiftance to the convex fide. Now, a cubic foot of air 

 weighs \\ oz. ; therefore, as 1^ : .241 1 : : 1 : .1929, which is the 

 bulk of the column of air whofe weight is equal to the refiftance, 

 which being divided by £ of a foot, the area of the bafe, we have 

 .86 feet for the altitude of that column, and which, therefore, 

 is nearly equal to the half altitude above found for the velocity, 

 exceeding it only by about the 13th or 14th part. 



13. \thly, But, from the fifth column, it appears, that the 

 altitude of the column of air, whofe preflure is equal to the re- 

 fiftance on the flat fide of the hemifphere, is to the altitude due 

 to the velocity of the body, as 2* to 2, inftead of being equal, 

 as required by the theory* 



VIL 



