414 i?. D. Oldham — Notes on a Graphic Table of Bijjs. 



(dotted in Fig. 1) till it cuts tbe side BC sX 34° from C; 34° is the 

 required dip. 

 Al 



Fig. 1. 



This method is in principle rigidl3f accurate, but the degree of 

 accuracy attainable in practice depends on the scale of the graticule 

 and the degree of care with which it is applied. 



For the solution of the other classes of problems, the scale of 

 tangents and co-tangents require to be extended so as to embrace 

 at least 60° of the quadrant and we require the circle round to 

 be completed ; in Fig. 2 I have given one-half only, as this will 

 be sufficient for explanatory purposes. 



30 ■ 40 so 60 70 -so 8Q "0 60 ,50, '.^O , ■ 30 



60- "^^ ■ '50 ,40 : 30, vSO' 10 10:2 30 ■ i-O, ;/,. 50 QO 



Fig. 2. 



(2) Given the apparent dip in two directions ; required the direc- 

 tion and amount of the true dip. 



(a) When both the dips are greater than the minimum angle on 

 the scale of cotangents ; the said scale to be used throughout. On 



