SOS ATMOSPHERIC ELECTRICITY. 



disappear in tlie clouds. We can in this way examine the state of 

 very high clouds, the electricity of which would be too feeble to act 

 in a sensible manner on apparatus placed at the surface of the earth. 



In reference to the great utility of the kite in researches on at- 

 mospheric electricity, it is necessary to take into consideration the 

 inconvenience of not being able to use it except during winds. In 

 calm weather we might substitute for it a balloon furnished with the 

 necessary additions, and retained by a cord which is a good conductor 

 of electricity. But this method of experimenting is much less simple, 

 because we can not always procure hydrogen gas, and because the 

 lateral currents bear the balloon to the leeward and prevent its rising 

 perpendicularly. We should also mention certain effects obtained by 

 the use of the kite, and which do not appear to be owing to the influ- 

 ence of atmospheric electricity, but to the induction of an electric cur- 

 rent on itself. It is well known that Mr. Henry,* [now Secretary of 

 the ^Smithsonian Institution,] has shown that a discharge of ordinary 

 electricity produces a powerful secondary current in the wire adjoining; 

 he thinks that ordinary electricity ought to produce an analogous 

 effect in the same wire when the discharge takes place ; and gives on 

 this subject the following experiment made on atmospheric electricity, 

 in 1836, by a committee of the Franklin Institute of Pennsylvania : 

 Two kites had been attached and raised with an iron wire in place of 

 cord ; tbe wire extended for the length of about a mile. The weather 

 was perfectly clear, and yet sparks drawn from the wire were of such 

 great pungency that fifteen persons joining their hands, and standing 

 on the ground, received the shock at the same moment that the first 

 touched the wire. On holding a leyden phial by its external coating, 

 and presenting the knob to the wire, a very strong shock was received 

 which was nothing but the result of an action of sudden and powerful 

 induction. According to Mr. Henry, these eftecls must not be at- 

 tributed to the electricity accumulated at the ends of the wire, for it 

 was necessary to approach the finger to about one-fitth of an inch before 

 receiving the spark ; he adds that we cannot attribute them to 

 quantity only, since Wilson's experiments have proved we cannot 

 produce the same .effect with an equal amount of electricity diffused 

 over the surface of a great conductor ; he concluded, therefore, that 

 the effect observed was owing to an induction of the current on itself. 

 The wire containing a considerable quantity of electricity of feeble 

 tension, which passed in the form of a current, it produced an induc- 

 tion at the end of the discharge, as in the case in which a long wire 

 transmits a voltaic current. To the same cause must be attributed 

 the remarkably pungency of the sparks, though very small, which are 

 received from a long conductor along which a feeble current of ordi- 

 nary electricity passes. 



The electro-atmospheric apparatus acquires great sensibility when 

 the insulated conductor is movable. De Saussuref states that he 

 obtained signs of electricity when he raised his electrometer, furnished 



* Contributions to Electricity and Magnetism, page 47. — From the Transactions of tlie 

 American Philosophical Society, vol. YI. 



t Voyages dans les Alpes, tom. II, § 799, p. 218. 



