234 AUEOEA BOREALIS, 



inci edible. Now we have found that, throughout a large portion of the torrid 

 zone, auroras have never been known to occur; while throughout a zone. sur- 

 rounding the magnetic pole they are seen almost uninterruptedly during the 

 period that the sun's light does not obscure them from our view. The aurora, 

 then, does not result from nebulous matter encountered by the earth in its pro- 

 gress round the sun. 



2 Auroral exhibitions take place in the upper regions of the atmosphere, 

 and partake of the earth's rotation. All the celestial bodies have an apparent 

 motion arising from the rotation of the earth ; but bodies belonging to ihc earth, 

 including the atmosphere and the clouds which float in it, partake of this rota- 

 tion, so that their relative position is not aifected by it. The same is true of 

 the aurora. AVhenever a corona is formed, it maintains sensibly the same posi- 

 tion in the heavens during the whole period of its continuance, although the 

 stars meanwhile revolve at the rate of 15^^ per hour. Auroral exhibitions are 

 therefore to be regarded as terrestrial phenomena. 



3. The light of the aurora is caused by the movement of atmospheric elec- 

 tricity. This is proved by its effect upon the telegraph wires. The electric 

 telegraph is worked by a current of electricity generated by a battery, and flow- 

 ing along the conducting wire which unites the distant stations. This current 

 flowing round an electro-magnet renders it temporarily magnetic, so that its 

 armature is attracted, and a mark is made upon a roll of paper. During a 

 thunder-storm the electricity of the atmosphere affects the conducting wire in a 

 similar manner, so as to set in motion the recording pen in the telegraph office ; 

 and thus, during a thunder-storm, telegraphing generally becomes quite impossi- 

 ble. A similar effect is produced by the presence of an aurora. During the 

 great aurora of November 17, 1848, the electro-magnets of the telegraph lines 

 were rendered magnetic, even when no A'oltaic battery was attached to them, so 

 that, for three hours, communication by telegraph was rendered impracticable.* 



During the aurora of September 2, 1859, the aurora caused so strong and 

 steady a current of electricity on the telegraph wires, that it was possible to 

 transmit telegraph messages by the use of this current without any- voltaic 

 battery whatever. During this aurora there were remarked all those classes ot" 

 effects which are considered as characteristic of electricity. 



A. In passing from one conductor to another, electricity exhibits a spark of 

 light. Dating the auroras of August 28 and September 2, 1859, brilliant sparks 

 were drawn from the telegraph wires, even when no batteiy was attached. At 

 Springfield, Massachusetts, a flash was seen about ha!f the size of an ordinary 

 jet of gas. At Boston, Massachusetts, a flame of fire followed the pen of Bain's 

 chemical telegraph. At Pittsburg, Pennsylvania, streams of fire were seen 

 when the telegraph circuit was broken. At Washington, D. C., a spark of fire 

 jumped from the forehead of a telegraph operator when his forehead touched a 

 ground-wire. Bright sparks were noticed on the conductors of the telegrapli 

 lines to Bordeaux, in France. On the telegraph lines of Norway sparks and 

 uninterrupted discharges were observed. t 



B. Ill passing through poor conductors electricity develops heat. During 

 the auroras of August 28 and September 2, paper and even wood were set on 

 fire by the auroral influence alone. At Boston, Massachusetts, a flame of fire 

 burned through a dozen thicknesses of paper. The paper was set on fire and 

 p:oduced considerable smoke. At Springfield, Massachusetts, the heat was 

 sufficient to cause the smell of scorched wood and paint to be plainly percepti- 

 ble. At Pittsburg. Pennsylvania, the magnetic helices became so hot that the 

 hand could not be kept on them. On the telegraph lines of Xorway, pieces of 

 paper were set on fire by the sparks of the discharges from the wires, and the 

 « — 



* Do La Rive's Elec, v. 3, p. 237. 



t Amoricau Journal of Scieace, a. s. , v. '31, p. 323. 



