Terrestrial Re jr action. 567 



than the value Q (c) = 478, for the corresponding heights and 

 small dips. If a more accurate formula than (54) is desired 

 for a particular height, the value of E/ given in Table' VIII., 

 or one calculated in a similar way to suit the case, should be 

 taken and substituted for R' (c) = 7497 in (54) . These formulae, 

 so obtained, will be accurate to 1 in 400 for zenith distances 

 in the approximate range 40°<<£ < 89° 30'. Probably the 

 lower limit can be much decreased in many cases. 



Table VIII. 



h. Q. 

 1km. --- 530 



E'. 



7642 



2 



505 



7570 



3 , 



487 



7520 



4 , 



468 



7467 



5 , 



450 



7418 



6 t 



431 



7367 





415 



7324 



8 , 



396 



7275 



Fiar. 7. 



*-05 



The error caused by replacing tan i) by Din (54), thus 

 obtaining Chauvenet's formula (49), is plotted in tig. < 



2 R 2 



