118 GEOGRAPHIC TABLES AND FORMULAS. [bull.214. 
Formula for using quantities S and T: 
log sin a — log a" -\- S. 
log tan a = log a" -f- T. 
log cot « = a. c. log a" -\- a. c. log 71 
log a" = log sin a .— 8 = log tan a — T. 
log cos a = log (90° — a)" -\- S. 
log cot a = log (90° - a)" + T 7 . 
log tan a = a. c. log (90 ( - a)" + a. c. log T 7 . 
log (90 - a)" = log cos a- S= log cot a - 71 
