36 PROFESSOR FORBES'S EXPKRIMENTS ON TERRESTRIAL MAGNETIC INTENSITY. 



east, of the Isoclinal lines with the meridian is, 



Arc whose tan ^ = 74.3 

 Sou 



Comparing the observations with the formula, 



0'.7114 * OM3665 y + 64 52' A, 



we have the following results : 



Difference. 



1.7 

 -1.7 



+ 3.7 



1.7 

 + 0.4 

 + 1.1 



Mean error (without regard to sign) I'. 7. 



