Gravity and Magnetism. 



55 



aether; others gradually, through the comparatively sluggish 

 vibrations of the air. 



VII. The comparative barometric disturbances of the sun and 

 moon exhibit an approximate mean proportionality between 

 their comparative differential- tidal and magnetic disturbances. 



Let the solar differential-tidal force be represented by A', and 

 the lunar by A", the respective barometric disturbances by B' 

 and B"; and the magnetic disturbances by M' and M". If M' 

 and B" are required, we have 



A'+A". B'. B". M'. M". 



Theoretical values, . . . . -00012 -00144 



Observed values, 2-55 -00057 -00013 -00140 -0000255 



VIII. The theoretical gravitation-variation of magnetism 

 (Prop. IV.) is slightly less, while the theoretical barometric varia- 

 tion (Prop. VII.) is slightly greater, than the corresponding 

 observed variation. The excess in one case exactly counterbalances 

 the deficiency in the other, the sum of the theoretical being pre- 

 cisely equal to the sum of the observed variations. 



IX. The total daily magnetic variations, like the barometric, 

 can be resolved into a variety of special tides, which may be 

 severally explained by well-known constant or variable current - 

 producing and weight-disturbing forces. 



Hours from 

 midnight. 



A. 



Theoretical 



gavitation- 



tide. 



B. 



Theoretical 

 different ial 

 solar tide. 



A+B. 

 Theoretical 

 mean tide. 



Observed 

 mean tide. 







6 



12 



-•00067 



•00000 



+•00067 



+•00024 

 -•00024 

 +•00024 



-•00043 

 -•00024 

 +•00091 



-•00043 



-•000231 



+•00095 



The hours are counted from midnight, in each half- day. 



Column A contains the hourly differences from mean weight, 

 attributable to solar gravitation, with changed signs — diminu- 

 tion of weight being accompanied by increase of magnetism, and 

 vice versa. 



The form of the tide in column B is evidently such as should 

 be determined by solar action. The magnitude of the tide is 

 estimated by comparing the relative amounts of motion down 

 the diagonal and down the arc of a quadrant 



(-00067 x [l-(|-i)]=-0004^Y 



The mean-tidal difference [(-00067- -00048) +- 2] is very nearly 

 equivalent to the average theoretical inertia-disturbance of weight. 



