OP ARTS AND SCIENCES. 27 



If, now, I electrify Bt negatively, it will attract and lift Bm, 

 and the index will move to the right. 



If, however, I at the same time electrify Lb positively, it will 

 tend to repel and lift Lm, and, as the repulsive lifting of Lm is 

 equal to the attractive lifting of Bm, the index will remain at 

 rest. That is, an attraction between Bt and Bm is balanced by a 

 repulsion- between Lb and Lm. 



If, now, I suddenly change the electrification of the beam of the 

 balance, and consequently of the plates Bm and Lm, to negative, 

 we have a repulsion between Bt and Bm, balanced by an attraction 

 between Lb and Lm. 



Now, it can be shown by purely mathematical reasoning from 

 electric phenomena, (see Maxwell's Electricity and Magnetism, 

 Chap. XIX.,) that an ether current flowing between two positively 

 electrified plates would, provided it possessed the electro-magnetic 

 properties of a current of electricity, diminish their repulsion. If 

 it flowed with the velocity of light, and had quantitatively, as well 

 as qualitatively, the electro-magnetic properties of a current of elec- 

 tricity, it would just neutralize the repulsion. 



If, on the other hand, it passed between two plates, one of which 

 was charged positively and the other negatively, it would just 

 double their attraction. 



If, instead of moving with the velocity of light, 300,000,000 

 meters per second, it moved only Yulixm as fast, or 30,000 meters 

 per second, the repulsion between similarly electrified plates would 

 be diminished by one part in ten thousand, and the attraction 

 between oppositely electrified plates increased one part in ten 

 thousand. 



Now, it can be further shown from purely astronomical measure- 

 ments that our balance is, on the 22d of December at noon, carried 

 through space with a velocity of 30,000 meters per second. 



Observations made at noon on that day, then, ought to show the 

 index of the balance one side of the position of equilibrium when 

 the movable plates are electrified positively, and the other side 

 when electrified negatively. The difference should indicate a total 

 change of force of one part in twenty-five hundred. 



This deflection of g^Vo ^ s tna ^ due simply to the rotation of the 

 earth around the sun. That due to the rotation of the earth about 

 its axis is too small to note. But the whole solar system is moving 

 towards Hercules with a velocity of 8,000 meters per second. 



On the 22d of March this velocity would have to be added to the 



