134 



ITERATIONS OF THE MOON. 



in addition to the tidal action, demonstrates the 

 electro-magnetic connection between the earth 

 and moon. 



The extent of the northern and southern libra- 

 tions of the moon, alternately toward the north 



and the south poles 

 of the earth, is prob- 

 ably governed by 

 the equatorial or di- 

 amagnetic currents, 

 which restrain the 

 moon from vibrat- 

 ing more than about 

 29 each side of the 

 equator. In Fig. 

 50, M represents a 

 magnet, and c a 

 helix coil, set afloat like the ring of De la Rive, 

 with the appended zinc and copper plates im- 

 mersed in acids. On bringing the magnet toward 

 the ring-coil, it is found to pass over the magnet, 

 as the eye of a needle is passed over a thread, and 

 continues to move over it until the ring arrives at 

 the middle part of the magnet. There it stops, 

 and remains permanently at rest. The earth, 

 being a magnetic body, represents M, and the 

 currents incident to the circling of the moon 

 in its monthly orbit around the earth, may repre- 

 sent the coil of conducting-wire, c. The recipro- 

 cal action and reaction between the diamagnetic 



