1826.] during the Act of Rotation. 449 



direction the needle has a tendency to assume according to the 

 law above-named, in consequence of the magnetism impressed 

 by the rotation in the line ti s. Beginning at the point A, if we 

 say the motion is from left to right, that is from n to n', it will 

 be from right to left at 60°, 75°, 90°, &c. till we arrive again at 

 30° ; at this point as at the former the new power is exerted in 

 the actual direction of the needle, and if it were greater than its 

 natural directive power, it would wholly invert it ; in this case 

 it would pass to either hand ; but as the new power cannot 

 invert it, it has no tendency to deflect it, and it therefore remains 

 stationary. Thus one of the results which was at first the most 

 perplexing, serves to confirm the law we have established. 



" On similar principles, if we conceive a circle passing verti- 

 cally from 90° to 90°, and if the needle be perfectly neutralized, 

 at different positions in this circle, and rendered parallel to the 

 axis at each, then in every case the needle will have a tendency 

 to take up a position directly at right angles to the axis of the 

 shell, and it will point in opposite directions at certain parts of 

 this circle : thus, if to fix the idea we conceive the axis to be iix 

 the meridian, and the motion of the shell from west to east, then 

 at the east point of the horizon the needle will point to the west, 

 and it will do the same at all points between the horizon and an 

 altitude of 60°; beyond this, the north end will point to the east 

 till we have passed the zenith 30° on the west side ; and then 

 again from this point to the west horizon the north end will 

 again point to the west ; and similar changes will take place 

 below the ball. This, which is a necessary consequence of our 

 hypothesis, is completely verified by experiment. 



" It is presumed, that what has now been stated is sufficient, 

 without referring to any further experiments, to establish the 

 principal fact adverted to in this letter, viz. that when any iron 

 body is put in rapid rotation on any line not coinciding with its 

 magnetic axis, a temporary derangement takes place in its mag- 

 netic powers, which in its effects is equivalent to a new axis of 

 polarization perpendicular to the plane passing through its axis 

 of polarization and rotation." 



{To he continued.) 



New Series, vol. xi. 2 g 



