X CONTENTS. 



FAGB 



North and South pointing of Compass Needles. The same 

 Compass Needle, when transported to either Pole of the Earth, 

 begins to dip till its Direction becomes perpendicular to the 

 Earth's Surface at the Pole. Diamagnetic Currents excite 

 Heat. Cause of Internal Heat of the Earth. Currents about 

 Molecules illustrated. 



CHAPTER XV. 



CIRCULATION OFj ELECTRIC CURRENTS IN CLOSED CIR- 

 CUITS 127 



The Tendency of all Fluids put yi Motion is to return to the same 

 Place, in strict Accordance with the Universal Law of Astron- 

 omy, in the periodic Return of each Heavenly Body to the 

 same Place. Closed Circuits are 'formed by joining the two 

 Ends of a horse-shoe Magnet by an Armature. Rings of Vapor 

 and spherical Bubbles are produced by similar Closed Cir- 

 cuits. The Circulation of the Diamagnetic Currents about the 

 Earth and Moon produces the Electro-Magnetic Action be- 

 tween them which causes the simultaneous Rise of the Tides 

 on both Sides of the Earth ; as illustrated by Fig. 49. The 

 Librations of the Moon are maintained by the Diamagnetic 

 Currents from extending so far as to pass beyond the Limits 

 of the Ecliptic. The Ascent of Sap in Trees by Capillary At- 

 traction is due to Circulating Diamagnetic Currents. 



CHAPTER XVI. 



MECHANICAL ACTION CONSIDERED AS A TEST OF ELEC- 

 TRIC EXCITATION. POPULAR THEORIES OF ELEC- 

 TRICITY 138 



The comparative Velocity of Transmission of Mechanical Action 

 by various Substances. Tenuity and Velocity of Electricity. 

 Transmission of Motive Power to a Distance through Con- 

 ducting Wires for Operating Machinery. Velocity an Equiva- 

 lent of Power. Imaginary Telegraph of Lucretius. 



CHAPTER XVII. 



EXTENT OF SOLAR ACTION TRANSMITTED TO THE SUR- 

 FACE OF THE EARTH 150 



Effective Power of Sunshine in lifting Water to the Sky as 

 Vapor. The ready Excitability of Water resembles that of 

 Air. Estimate of the Volume and Force of the Cataract of 



