1826.] .y^ ^^'<<^x>armng from its Rotation, -^ . 41 



*< 2d. It decreases as the plate approaches the pole, and is 

 between the latitudes 50° and 60°, apparently very nearly at bb^ ; 

 and from this point it increases till it attains a maximum in a 

 contrary direction at the pole. 



** 3d, At the south pole and on each side down to the latitude 

 bdi°, the deviation of the south end of the needle due to rotation 

 is in the direction of the north or lower edge of the plate ; or, 

 from the south pole down to the latitude 55°, the south end of 

 the needle moves toicards the plate, when the inner edge of the 

 plate moves from the south pole, and from the plate when the 

 inner edge moves towards the south pole. 



**4th. From the equator towards either pole as far nearly as 

 the latitude db^j the south end of the needle moves in the direc- 

 tion of the south edge of the plate ; that is, it moves towards the 

 plate when the inner edge of the plate moves towards the south 

 pole, B.nd from the plate, when that edge moves from the south 

 pole; also the north end of the needle moves towards the plate, 

 when the inner edge moves toicards the north pole, and from the 

 plate, when that edge moves from the north pole. Consequently 

 towards whichever pole the inner edge moves, the corresponding 

 end of the needle will move toivards the plate from the equator 

 to the latitude of 55° nearly, and the contrary will take place 

 from the latitude 55° to the pole. 



" The observations which I made with the plate on the north 

 side of the equator, though not so multiplied as those on the 

 south, were sufficient to show, that the deviations due to rota- 

 tion observed the same laws on that side of the equator as I had 

 noticed on the south side. 



"The deviation due to the rotation of the platCj when its centre 

 is in the secondary to the equator and meridian, having a pecu- 

 liar character, namely, two greater maxima when the centre is 

 in the equator, two less maxima, in a contrary direction, when 

 the centre is in either pole, and four points where it vanishes, I 

 consider to be particularly well adapted for forming an estimate 

 of the correctness of any theory which may be adopted for the 

 explanation of the pha^nomena in general ; since the theory must 

 be perfectly compatible with these peculiarities, before it can be 

 applied to the explanation of the less marked pha^nomena. 



" As it appeared from these observations, that the point 

 where the deviation due to rotation vanishes, is not far from lat. 

 55°, the complement of which, 35°, is nearly half the angle of 

 the dip, I wished to ascertain whether the deviation were really 

 in latitude 54° 45', which I considered to be correctly the 

 complement of half the dip 70° 30', although I could not see 

 how the angle which the plane makes with the horizon could 

 have an influence on an angle in the plane itself. Subsequent 

 observations showed, that in this instance the deviation due to 

 rotation vanishes, or nearly so, when the polar distance of the 



