

THUNDER-STORMS. 



The Deficiency of our present Knowledge. Of common Thunder-Clouds. Character and Electric 

 Charge of Clouds. Discharge between vicinal Clouds. Conditions for such Discharge. Discharge 

 between the Clouds and the Earth. Mutual Attraction or Repulsion of Electrized Clouds. Char- 

 acters of the upper and of the lower Surface of Clouds. Negative Testimony, respecting Thun- 

 der from an isolated Cloud. Cases of Lightning from an isolated Cloud. Afresh Case related by I 

 M. Duperrey. Obvious Inferences from the above Cases. Of Volcanic Thunder-Clouds. ( 

 Lightning from the Ashes, Smoke, and Vapor of Volcanoes. Theoretical Ideas of its Origin. < 

 Of the Height of Stormy Clouds. Mode of Observation. Ascending Flashes of Lightning. Mi- < 

 nor Limits of the Height of Storm-Clouds. Inefficiency of many recorded Observations. Table 

 of Observations as collected by Arago. Flash of Lightning from a Cloud upward. Of Light- 

 ning. Varieties of Lightning. Zigzag Lightning. Forked Lightning. Deficiency in our Vo- 

 cabulary of Terms. Sheet Lightning. Table of Instances of Ball-Lightning. Mr. Harris's 

 Explanation of Ball-Lightning. On the Speed of Lightning. Theory of Vision illustrated by 

 a rotating Disk. Wheatstone's Experiments. Observations of the Velocity of Lightning. 

 Silent Lightning. Heat Lightning. Thunder Bursts. Of Luminous Clouds. Clouds them- 

 selves faintly Luminous. Possession of the duality in various Degrees. Clouds visibly Lumin- 

 ous. Various Observations of luminous Clouds. Sabine's Observations. Of Thunder. Rolling 

 of Thunder. Duration and Intensity of rolling Thunder. Violent Thunder from Ball-Lightning. 

 Interval between Lightning and Thunder. A case in which they were almost simultaneous. 

 Thunder without Lightning. Noise attendant on Earthquakes. Of the Attempts to explain the 

 Phenomena of Thunder and Lightning. Identity of Lightning and Electricity. Whether pon- 

 derable Matter, or a Propagation of Undulations. Difficulties of the Undulatory Hypothesis. 

 Bull-Lightning and the Inferences to which it leads. Bituminous' Matter accompanying a Case 

 of Lightning Discharge. Explanations of silent Lightnings. Observations of silent Lightnings. 

 Difficulties in the Explanation of silent Lightnings. Arago's Suggestion for Observations. Light- 

 ning hidden by dense Clouds. Place of the Sound of Thunder. Greatest Distance at which 

 Thunder is heard. Case of Distance beyond which it was Inaudible. Distance at which other 

 Sounds have been heard. Effects of Heat, Cold, Wind, &c. On the Transmission of Sound. 

 Thunder heard when no Cloud was Visible. Hypothesis of the Cause of Thunder from the Cre- 

 ation of a Vacuum. Contractions and Dilatations of the Air assigned as the Cause. Ponillet'a 

 Theory of Decompositions and Recompositions. Influence of Echo in causing the Roll. Dura- 

 tion of an Echo. Duration of the Roll of Thunder at Sea. Dr. Robison'a Explanation of the 

 Roll. Application of the Theory to Zigzag Lightning. Inefficiency of the Theory. Means of 

 obtaining a Minor Limit of the Length of a Flash. 



