1864.] 



495 



[Chase. 



LUNAR-DAILY DISTURBANCES OF MAGNETIC FORCE AT ST. HELENA, IN 

 MILLIONTHS OF THE TOTAL FORCE. 



The above table shows, that 



1. The moon's attractive force (M-v-R'^=.016-^60===.000004) 

 multiplied by the coefficient of its differential attraction (2.5,5) gives 

 .0000113, which is nearly the same as the mean meridional magnetic 

 disturbance [(.000005 + .000016)-t-2=.0000105]. 



2. The increase of magnetism at 12h. is nearly equivalent to the 

 attractive force, multiplied by the square of the distance from the 

 centre of gravity of the system, and divided by the square of the 

 earth's radius (.000004x7707''-^-3963^=.0000168). 



3. There is a tendency to equality of disturbances on each side of 

 the meridian at Ih. and 8h., as in the solar magnetic tide. 



4. The greatest disturbance occurs at the hours of lOh. and llh. 

 P.M., both in the solar and in the lunar tide. 



5. There are some indications of an increase of gravity and de- 

 crease of magnetic force when the tidal flow is towards the centre 

 of gravity of the terrestrial system, and vice versa. 



6. The rotation-tide has the customary quarter-daily phases of 

 alternate increase and diminution. 



X. The phenomena of magnetic storms indicate the existence of 

 controlling laws, analogous to those which regulate the normal 

 fluctuations. See Proceedings Amer. Philos. Soc, Oct. 21, 1864. 



The foregoing comparisons have been based on General Sabine's 

 discussions of the St. Helena records. It would be desirable, if it 

 were possible, to confirm them by observations at other stations near 

 the equator, but the need of such confirmation is in great measure 

 obviated by the variety of ways in which I have shown the probable 

 connection of gravity and magnetism. At extra-tropical stations, the 

 rotation tide becomes so preponderating that it is difficult to trace 

 the diminished gravitation- and differental-tides, still I shall look con- 

 fidently to a fuller development of the theory of tidal action, for future 

 additional support to my views. 



