1 1 8 CAUSES which afeff the ACCURACY 



/ 



V its value, I+s T+Aa . . It is found by making as j- to 



q 



. 

 r)J , f tw i ce the height, computed by the ordi- 



nary method, to a fourth proportional, which is to be added to 

 that height. 



THE correction for the diminimed gravity of the air is a 

 third proportional to the femi- diameter of the earth, and the 

 height, as computed by the ordinary rule. For different moun- 

 tains, therefore, this correction is in the duplicate ratio of their 

 heights. 



THESE corrections are both additive, and for fuch a moun- 

 tain as Coracon may be equal, the fir ft to 42, and the fecond to 

 12 feet. 



33. IN the meafurement of depths below the furface of the 

 earth, /3 is greater than #, and v = i, fo that the compreffing 



/ r sx .\ l+n 

 force, at any depth x below the furface, is = (J - J*J , 



where the fluent is affirmative, not negative, as in all the pre- 

 ceding inftances, becaufe the air* which, by its weight, com- 

 preffes the ftratum at the depth x, is on the fame fide of that 

 ftratum with #, whereas it was before on the oppofite fide. 



Making, therefore, y = T+A* , we have, 



p(i m) 



by proceeding as above, 

 H+b x p*i ,H+b 



In 



