184 ELEMENTS OF STATIC ELECTRICITY. 



the two effects. But if one be placed opposite the 

 center of the cylinder or spheroid, so that its action is 

 at right angles to that of the other, the intensity of 

 action at the ends is diminished. 



In the sun, moon, and earth, these conditions are 

 exactly fulfilled as to shape and position ; and, prob- 

 ably also, as to difference of potential. The earth is 

 an oblate spheroid, whose longer axis lies east and west ; 

 pointing nearly to the apparent path of the sun and 

 moon. Hence at the full moon, the new moon, and 

 the quarters, we must have the same inductive effects 

 as in the experiment with the spheroid and the two 

 spheres. The earth, at full moon, is between the sun 

 and moon, and receives the highest inductive effect. 

 At new moon they are on the same side of it, and 

 nearly in line, and their effect, if at different potentials, 

 is lessened : while, at the quarters, when the induction 

 from each is at right angles to that of the other, it is at 

 its minimum. Hence we should expect to find, as in the 

 ocean tides, electric neap and spring, ebb and flood tides. 



Very little is known of the relative inductive influ- 

 ence of the sun and moon on the earth. Judging from 

 the analogy of the ocean tides, we might infer that the 

 induction of the moon is greatly in excess of that of 

 the sun. But in estimating effects produced by gravity, 

 the two principal factors are mass and square of dis- 

 tance; whereas, in estimating inductive electric effects, 

 the various agencies by which electricity is generated 

 must also be taken into account. 



The nearness of the moon to the earth causes its 

 effect on the ocean tides to be much greater than that 

 of the sun, though its mass, as compared with the mass 

 of the sun, is only as 1 to 26,400,000. But, in consid- 



