xxvi CONTENTS. 



Vibrations ; Mechanical effects of vibrations, 502. Chemical effects ; Comparison 

 with sound, 503. General inferences ; Additional remarks ; Thermomultiplier ; 

 Rock salt, 504. Polarization of light and heat ; Discoveries of Melloni and 

 Professor Forbes, 505. Theory of Heat ; References, 506. 



LECTURE LIIL 

 ON ELECTRICITY IN EQUILIBRIUM, 507. 



Utility of electrical hypotheses ; Division of the subject, 507. Supposed elec- 

 tric fluid; Its attractions and repulsions, 508. Conductors and nonconductors; 

 Positive and negative electricity ; Local electricity, 509. Distribution of electri- 

 city; Electricity of a sphere; Connected spheres, 510. Difference of hydrostatic 

 and electrical pressure; Attractions and repulsions, 511. Induced electricity; 

 Neutral point ; Effects of attraction and repulsion ; Currents of air ; Bodies elec- 

 trified in different degrees, 512. Charge; Discharge; Shock; Coated jar; Bat- 

 tery; Comparison of conducting powers, 513, 514. 



LECTURE LIV. 

 ON ELECTRICITY IN MOTION, 516. 



Effects and causes of electrical motions, and electrical apparatus ; Velocity ; 

 Spark, 516. Perforation of a jar ; Direction of the motion ; Opinions respecting 

 positive and negative electricity; Effects of electricity; Accumulation; Simple 

 current, 517. Electric light ; Heat, 518. Mechanical effects ; Chemical effects ; 

 Sensible effects, 519. Excitation of electricity; Electrics; Vapours; Tourmalin, 

 520. Galvanic electricity ; Chemical changes ; Galvanic combinations ; General 

 laws, 521. Particular facts ; Pile of Volta, 522. Troughs; Animal electricity; 

 Mr. Davy's discoveries, 523. Electrical nature of chemical attractions, 524. 

 Theory of the pile ; Efficacy of decomposable substances ; Electrical machines ; 

 Teylerian machine, 525. Electrophorus ; Cendenser ; Multiplier, 526. Doublers ; 

 Electrical balance; Quadrant electrometer ; Gold leaf electrometer, 527. Lane's 

 electrometer ; General observations, 528. 



LECTURE LV. 

 ON MAGNETISM, 531. 



Resemblance of magnetism and electricity ; Theory, 531 . Conducting powers ; 

 Magnetical substances, 532. Aurora borealis ; North and South poles ; Attrac- 

 tions and repulsions ; Polarity, 533. Arrangement of filings ; Directive force ; 

 Terrestrial magnetism ; Compass ; Dipping needle, 534. Illustration ; Temporary 

 magnetism ; Natural magnet ; Magnetic poles of the earth ; Diurnal changes, 535. 

 Variation of the declination ; Line of no declination ; Dip, 53G. Artificial mag- 

 nets ; Double touch, 537. Magnetic paste ; Division of a magnet ; Striking and 

 ringing a magnet; Hammering brass ; Solution in an acid, 538. Resemblance of 

 polarity to crystallization ; Additional remarks ; Discovery of Professor Oersted ; 

 Electro-magnetism, 539. Construction of the galvanometer ; Gumming; Nobili; 

 Action of the voltaic current, 540. Electro-magnetic telegraph ; Faraday ; Mag- 

 neto-electric machine, 541 ; Arago ; References, 542. 



