NATURAL PHILOSOPHY. 103 



peated at different elevations by some of our modern aeronauts, since 

 the results obtained would have an important bearing on the theory 

 of atmospheric electricity. Prof. Henry, Report of Smithsonian In- 

 stitution, 1859. 



ELECTRICITY GENERATED BY EVAPORATION. 



Mr. Pahniere, in a note in the Cosmos (Paris), states that in order 

 to obtain electricity by condensing vapors, he had some water in a 

 capsule of platina, not insulated, made to boil slowly. He collected 

 the vapor upon a platinum refrigerator, at a height of about two feet 

 above the surface of the water, and by means of a condensing elec- 

 troscope soon convinced himself that the vapor manifested positive 

 electricity. Encouraged by this result, he next sought to discover 

 the negative electricity in the capsule of platinum which contained 

 the water in a state of vaporization. Having isolated the capsule, 

 and put it in connection with a condensing electroscope, he concen- 

 trated the solar rays on the distilled water in the capsule by means 

 of a lens about a foot in diameter. He thus obtained a superficial 

 ebullition, hardly visible, and also indications of negative electricity 

 in the capsule. He afterwards varied the mode of experimenting, 

 and operated on different liquids. 



WHAT IS HEAT-LIGHTNING? 



The flashes of lightning often observed on a summer evening, un- 

 accompanied by thunder, and popularly known as " heat-lightning," 

 are merely the light from discharges of electricity from an ordinary 

 thunder-cloud beneath the horizon of the observer, reflected from 

 clouds, or perhaps from the air itself, as in the case of twilight. Mr. 

 Brooks, one of the directors of the telegraph line between Pittsburg 

 and Philadelphia, informs us that, on one occasion, to satisfy himself 

 on this point, he asked for information from a distant operator dur- 

 ing the appearance of flashes of this kind in the distant horizon, and 

 learned that they proceeded from a thunder-storm then raging two 

 hundred and fifty miles eastward of his place of observation. Prof. 

 Henry. 



EXPLANATION OF CERTAIN FAMILIAR ELECTRICAL PHENOM- 

 ENA. 



After the introduction of furnaces for heating rooms by warm air, 

 the public were surprised at exhibitions of electrical excitement 

 which previously had not been generally observed. If our shoes be 

 very dry, and we move over the surface of a carpet, with a shuffling 

 motion, on a very cold day, particularly in a room heated by a fur- 

 nace, the friction will charge the body to such a degree that a spark 

 may be drawn from the finger, and under favorable circumstances a 

 jet of gas from a burner may be ignited. There is nothing new or 

 wonderful in this experiment ; it is simply an exhibition of the pro- 

 duction of electricity by friction, which only requires the carpet, the 

 shoes, and the air to be dry conditions most perfectly fulfilled on a 



