454 DR. C. CHRBE, EXPERIMENTS ON ANEROID BAROMETERS 



TABLE VII. Katios of Mean Differences to Mean Difference in Range 30-21, 



Assume now that the ratio of the mean difference d n for a range of n inches to the 

 mean difference d 9 for a range of 9 inches is given by 



d n /d a = (n) = b -\- b t 



(4). 



Determining b , b lt b 2 from the three ranges in Table VII. common to all four 

 aneroids, we find 



<f> ( n ) = -028 + '053/1 + '0068n 2 ....... (5), 



with of course 



0(9) =1. 



In arriving at this expression, we utilised only the data from the three shortest ranges 

 in Table VII. Thus a check on the general suitability of the formula is supplied by 

 the good agreement between the mean results for the two longest ranges in the table 

 and the corresponding values 



= 1-587, 0(15) = 2-297 



calculated from (5). 



12. As illustrating the practical application of (4) and (5), suppose we find that 

 in a particular aneroid the mean difference between ' the descending and ascending 

 readings for the range 30-15 inches is 0'338 inch. Then we should conclude 

 that the mean difference for a range of m inches, m being any specified number, is 

 given by 



3,= '338 X <f>(m) -r- 0(15). 

 For instance, we should find for this aneroid 



J 4 = '043, J 6 = -078, J 7 = -099, 3 9 = '147, 3 12 = '234. 



