12 



CONTENTS OF VOLUME II. 



Necessity of Continuity in a Conductor. Effects proceeding from the Surface of the Earth. As- 

 cent or Ebullition of Water. Inundations from subterranean Sources. Mosaic Account of the 

 Deluge ; Analogous natural Phenomena. Electrical State of the Atmosphere favorable to the 

 Process of barking Trees Effect of Thunder on fermented Liquors, &c. Return Stroke reported 

 by Brydone. Theory of such Effects. Flame appearing on the Ground. Not extinguishable by 

 Water. Superposed Clouds not necessary to its Appearance. Stationary luminous Appearance. 

 Lightning rising from the Earth like a Rocket. Flames observed on exposed Points. Lumin- 

 ous Rain. Cases collected by M. Arago. Luminous Dust. 



POPULAR FALLACIES PAGE 83 



Fallacious Indications of Senses. Errors of the Sense of Feeling. Erroneous Impressions of Heat 



and Cold. Explanation of these by the Principle of Conduction. Why a Fan is cooling, Feats 

 - of the Fire-King explained. Horizontal Appearance of the Sun and Moon. Deceptive oval Disk 



in the Horizon. Deceptions of Vision of Taste of Smelling. 



PROTECTION FROM LIGHTNING 97 



Danger Proportionate to the Magnitude, not to the Frequency of the Evil. Ancient Methods of 

 averting Lightning. Persons in Bed not secure, as some think. Augustus's sealskin Cloak as a 

 Lightning Protector. Influence of Color on the Electric Fluid. Tiberius's Crown of Laurel as a 

 Lightning Protector. The Danger of taking Shelter beneath Trees. Futility of taking Shelter 

 in Glass Cages. Metal about the Person destroyed by Lightning. Metal Appendages to be laid 

 aside. Lightning Explosions occur at the Points where it leaves or enters a Metal. Part of a 

 Room which is most Safe. Lightning more likely to discharge among a Crowd than on a single 

 Individual. Influence of the Vapor of Transpiration, &c. Certain Individuals are comparative 

 Non-Conductors. Thunder-Clouds have been traversed with Impunity. Thunder-Storms below 

 the Place of Observation. PARATONNEKRES, or Lightning Conductors. Lightning Conductors 

 protective even when no Flash strikes them. Sparks at the Interval where a Conductor is dis- 

 jointed. Lightning Conductors drain off the Electricity of Clouds. Sparks or luminous Aigrettes 

 on the Points of Conductors. More frequent Occurrence at Sea. Influence of Elevation of a 

 Paratonnerre. Experimental Illustration. Electric Kites Captive Balloons as Paragreles and 

 for Meteorological Research. Pointed and blunt Conductors. Quantity of Lightning drawn down 

 by a Conductor. Mr. Harris's Conductors for Ships. Assumed Extent of the protecting Power 

 of a Paratonnerre. Not based on experimental Grounds. Cases against its general Application. 

 Lightning does not alway strike the highest Points. Lightning Conductors with many Points. 

 A Lightning Conductor must have sufficient Capacity. A Lightning Conductor must be in good 

 Connexion with the moist Sub-Soil. Charcoal Beds to receive the Base of the Conductor. Vici- 

 nal metallic Conductors. Conductors of metallic Wire-Rope; Insulation not needed. Conductors 

 for Powder Magazines. Efficacy of Lightning Conductors. Lateral or divided Discharge de- 

 fined; its Cause. More readily obtained from Conductors than from Leyden Discharges. Line 

 or Lines of least Resistance. Absolute Necessity of connecting the Conductor with vicinal Bodies. 

 Artificial Means of producing the Electrical Odor. Chemical Changes. Fusion. Fulgurites. 

 Mechanical Effects. Effects of conducting Bodies. 



MAGNETISM 109 



Magnetic Attraction and Polarity. Magnetic Meridian, Variation. Dip of the Magnetic Needle. 

 Magnetic Attraction known to the Ancients. Invention of the Mariner's Compass of uncertain 

 Date. Discovery of the Variation. Tables of Variation constructed. Robert Norman discovers 

 the Dip. Invention of the Dipping Needle. The Variation of the Variation discovered. Influ- 

 ence of Magnets on soft Iron observed. Polarity of Magnets observed. Construction of artificial 

 Magnets. Magnetism imparted to Iron by the Earth. Laws of Magnetic Attraction discovered 

 by Coulomb. Methods of making artificial Magnets consequent Points. Knight's improved 

 Method. Duhamel's Improvement. Coulomb's Researches on artificial Magnets. Influence of 

 Heat on Magnetism. Local and periodical Changes of the Variation. Diurnal Variation. Cas- 

 sini's Observations at Paris. Advancement of Magnetic Geography. Magnetic Equator. Mag- 

 netic Poles. 



ELECTRO-MAGNETISM 117 



Electro-Magnetism very recently discovered. Oersted's Experiments at Copenhagen. The Law 

 according to which the Needle is deflected. The Law of Attraction and Repulsion of Electric 

 Currents. Supposes Electric Currents circulating round the Globe. Arago shows that the con- 

 ducting Wire has Magnetic Properties. Needles magnetized by the Electric Current. The 

 Variation of the Attraction of the Current at different Distances determined. Laplace reduces 

 this result to an analytical Formula. The whole Body of Electro-Magnetic Phenomena reduced 

 to analytical Calculation. Faraday's Researches. Rotation imparted to Mercury by means of the 

 Magnet and Electric Current. The Multiplier or Galvanometer. Its Construction and Applica- 

 tion. The Earth affects Electric Currents in the same Manner as it affects Magnets. Ampere's 

 Theory of Terrestrial Magnetism. Researches of M. de la Rive. Magnetizing Power of the 

 Current at different Distances, and the Law of its Variation. The Effect produced by transmit- 

 ting it through Metals. The undulatory Theory of Electricity similar to that of Light. Thermo- 

 Electricity. Thermo-Electric Effects observed by Professor Seebeck. His Experiment with 

 Antimony and Copper. Researches of Yelin, Marsh, and Gumming. Oersted and Fourier con- 

 struct a Thermo-Electric Pile. Becquerel decomposes Water with such an Instrument. Thermo- 

 Electric Scale of Metals. 



THE THERMOMETER 129 



1 Advantages of a mercurial Thermometer. Method of constructing one. To purify the Mercury. 

 Formation of the Tube. To fill the Tube. Determination of the freezing and boiling Points. 



