1839] 



Terrestrial Magnetic Force in Southern hid'ia. 



241 



Calicut. — Observation coincident — 



a -I- 2 42 43 



TeUichernj, — The observations made at this place are so singularly dis 

 cordant, that they had better stand over for the 

 present. 



The above values of the dip, when laid down upon a map, exhibit an 

 appearance something reseraVding a series of parallels of latitude, — save 

 that the errors of observation (wlii; h soniewhat disturb their uniformi- 

 ty), prevent our discovering if these lines he parallel to the equator, or 

 if their inclination tends towards it on the eastern, or on the western 

 side of the Peninsula. To arrive at a more correct knowh'dge of this 

 matter, we will in the first place suppose them to be parallel, and pro- 

 ceed to find the latitudes of the magnetic equator, corresponding to the 

 several longitudes, from the well known formula 



where ^ represents the dip and \ magnetic the latitude of the place. It 

 may be objected— that this forinula obtains only on the old hypothesis, 

 of there being two magnetic })oles synnnetrically situated in a dianieter 

 of the earth, and near to its centre, — an hyi)othesis which is not com- 

 pletely borne out by our present improved knowledge : — however valid 

 this objection maybe with reference to high latitudes; a sli^^ht consi- 

 deration of the subject, renders it clear, that in the case of our observa- 

 tions (which twice cross the magnetic equator), a result very nearly ap- 

 proaching to the truth will be obtained by this formula: accordingly w^^ 

 get as follows— 



ian b 



— 2 ta)i \ 



