356 ATMOSPHERIC ELECTRICITY. 



"5 o'clock 12 minutes, evening. — The electricity becomes negative. 



"5 o'clock IS minutes, evening. — The electricity decreases considerably with the rain ; but 

 continued negative, and this for a long time, after the rain had completely ceased." 



The sudden passage from the strongest positive to the strongest nega- 

 tive electricity is certainly the most remarkable fact in the electrical 

 variations which were exhibited while the last storm continued. 

 Schiibler observed that this phenomenon is not rare in stormy weather, 

 and it ordinarily occurs after vivid flashes of lighting or during the 

 sudden showers which often accompany them. This remark of the 

 German philosopher is confirmed by the observations of M. Peltier,* 

 made by means of the rheometer. "On the 16th of June, 1836," 

 he writes to the Academy of Sciences of Paris, "I was awakened at 

 two o'clock fifteen minutes in the morning; a storm was raging on 

 all sides ; I ran to my instruments ; they denoted 80° of a negative 

 descending current ; the vivid flashes of lightning produced only ten 

 to fifteen degrees of decrease of deviation. At 2 o'clock 30 minutes 

 the negative current denoted 70°, when a very powerful flash of light- 

 ning occurred ; the needle whirled about and stopped at 80° on the 

 other side, where it remained thirty seconds ; then it returned to 70°. 

 The storm passed ofi* about 2 o'clock 45 minutes ; the needle returned 

 to its zero ; then passed to the positive side, where it remained." 

 The sudden changes which occurred in the intensity of the electricity 

 at tlie instant of the appearance of the flashes of lightning were 

 also observed by this philosopher. He speaks thus on this sub- 

 ject in the same note: "The storm of August 4, 1836, was entirely 

 diflerent from any other ; at 2 o'clock in the morning the electricity 

 was at first positive and then negative ; the needle advanced gradu- 

 ally towards its maximum ; then a flash of lightning occurred, and 

 the needle fell back half way ; then recommenced its ascending course 

 until the next flash of lighting, which made it retrograde. The 

 progressive course so entirely coincided with the electric changes 

 that I could foretell them by the fall of rain detaching itself from the 

 cloud." 



We have already said that Volta and De Saussure observed the 

 frequent succession of the two electricities exhibited by the elec- 

 trometers when they were exposed to the action of thunder clouds. 

 This frequency of the phenomenon did not escape M. Peltier's obser- 

 vation, who cites, among others, the storm of the 6th of August, 

 1836, as having exhibited to him at least twenty-five changes. Voltaf 

 sought for the cause of these changes in the electrical induction which 

 thunder clouds must naturally exercise on each other. If it be sup- 

 posed that while a cloud positively electrified produces in the electro- 

 meter a positive divergence, another cloud possessing a stronger 

 electricity, but of a contrary nature, happens to come above the 

 former, the electricity of the stronger will, according to Yolta, neu- 

 tralize, at a distance, that of the weaker, and will drive, into its lower 

 part, the electricity opposite to that which existed there at first ;^ or 

 rather the morepowertul electricity, after having caused the neutralizing 



'- Oomptes Rendus, tome III, page 147. 



■j- Journal de Physique, tome LXIX, page 343. 



