134 



AKSEL S. STEEN. TERRESTRIAL MAGNETISM. [NORW. POL. EXP. 



we obtain 



a = 209 33' 



p = - 61-5' 



In order now to be able to calculate by formula (4) the 4 corresponding 

 to any inclination-determination, it will clearly be necessary to know the 

 total intensity. It is true that during the expedition, observations with the 

 Fox apparatus for the calculation of the total intensity were also generally 

 made simultaneously with the inclination determinations; but since the result 

 of these as will presently be more fully explained - - can hardly be 

 regarded otherwise than as a failure, the horizontal intensity may be intro- 

 duced into formula (4) instead of the total intensity the former having 

 been determined by separate observations independent of the Fox appa- 

 ratus , and we may put 



W = 

 whereby we obtain 



H 



cos (/' + J) ' 

 p cos(I' 



= ^ -i 



H 



, T , . 



COS (I' + ), 



an equation which may easily be solved with regard to 4, when that quantity 

 is assumed to be sufficiently small to allow of putting cos 4 = 1, and 

 sin 4 = 4 sin 1'. The final formula for 4 then becomes 



p . cos (!' -\- a) cos I' 



~ H + p cos (/' + a) sin I' sin 1' 



(5) 



By the aid of this formula, I have calculated the following table, which 

 gives 4 for needle B, in minutes, for every degree of /' from 83 to 87, 

 and for every 5th unit in the 3rd decimal place of the horizontal intensity 

 from H =0-035 to JT=0'070. 



