1865.] 155 [Chase. 



d. Axis variou!^!// inclined. 



26. If the inclination of the axis to the meridian is less, or jrreater, 

 than 45°, the results approximate respectively to those obtained when 

 the axis is in the meridian, and when it is in the equator. 



C. Apparatus- Polarity. 

 Friction and the jarrin^r of the apparatu.s, modified by the degree 

 of velocity imparted to the ring, produce a polarity of their own 

 which should be carefully estimated, and due allowance made for its 

 influence in all delicate and doubtful experiments. In order to deter- 

 mine the directivity of the normal vibrations, independent of any 

 mere current influence, the needle was shielded by a glass, as in the 

 ordinary surveyor's or mariner's compass. 



27. When the axis is in the meridian, the polarity appears to be 

 meridional. 



28. With the axis in the equator, the polarity is also meridional. 



29. If the northern extremity of the axis is inclined to the west, 

 the needle declines to the east. 



30. Giving the axis an easterly inclination, the needle declines to 

 the west. The declination is, therefore, from the axis in all cases, 

 and we may infer that the earth's rotation exerts a constant tendency 

 to increase the normal declination of the needle. 



31. In all positions of the axis there appears to be a slight dispo- 

 sition in the needle to decline to the east, independent of the motion 

 produced by the mere vibration of the apparatus. If this disposi- 

 tion is owing to terrestrial currents, it is probable that the declina- 

 tion would be westward in the southern hemisphere, in accordance 

 with Ferrel's law, that, " in ichatever direction a hody moves on the 

 surface of the earth, there is a force cjrisincj from the eartli's rota- 

 tion which defects it to the right in the northern hemisphere, but to 

 the left in the southern." (Math. Monthly, i, 307.) 



32. If a candle-flame, or the smoke of an extinguished taper, be 

 brought near to the revolving ring, it will be repelled from the equa- 

 tor, attracted to the poles, and neither attracted nor repelled at a dis- 

 tance of about 30° from the equator. 



33. If a magnetic needle is substituted for the taper, it tends to 

 parallelism with the axis at the equator, and dips towards the centre 

 as it approaches the poles, in accordance with its general disposition 

 to range itself in the line of strongest vibration. (Exp. 3, Proc. 

 A. P. S., ix, 359.) 



