Chase.] J^gg [October. 



D. Revolving Discs attached to the Ring. 

 a. Discs Axial. 



34. Whatever may be the position of the axis, there is a very 

 slight axial polarity. 



b. Discs Perpendicular to Axis. 



35. There is no current-polarity. 



c. Discs with 45° East Declination. 



36. If the axis is in the meridian, the needle declines to the east. 



37. If the axis is in the equator, when the top of the ring moves 

 south the needle declines to the east, but when the ring moves north 

 the declination is westerly. 



38. If the axis is inclined to the meridian, and the disc passes 

 over the needle in the magnetic equator, the declination is easterly ; 

 but if the disc is meridional, I am unable to discover any decided 

 current-polarity. 



d. Discs with 45° West Declination. 



39. Placing the axis in the meridian, the needle declines to the 

 west. 



40. When the axis is equatorial, the declination is westerly. 



41. When the axis is inclined to the meridian, and the disc is 

 equatorial, the needle declines to the west; but if the disc is me- 

 ridional, it produces no marked polarity. 



42. All of the experiments with revolving discs, as well as many 

 of those with fixed discs, appear to be affected by changes in the 

 earth-currents, especially when the motion of the ring is northerly. 



The foregoing results are in precise accordance with the theoretical 

 deductions contained in my papers on the "Numerical Relations of 

 Gravity and Magnetism," on the " Influence of Gravity on Mag- 

 netic Declination," and on " Gravity and Magnetic Inclination " 

 (Amer. Phil. Soc, Dec. 16, 1864, April 21 and May 19, 1865, and 

 Amer. Jour, of Science [2], xxxix, 312 ; xl, 83, 166), as well as 

 with Dove's discovery that analogous atmospheric states are more 

 frequently found under the same meridian than under the same 

 parallel, and with Ferrel's demonstrations of the tendency in fluids 

 gyrating normally to move towards the pole, the parabolic route of 

 cyclones, the lateral pressure of moving bodies, and the disposition 



