[ 511 ] 



LXIX. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued fi'om p. 461.] 



June 19, 1856.— The Lord Wrottesley, President, in the Chair. 



THE following communication was read : — 

 " On the Aurora." By Reuben Phillips, Esq. 

 In this paper the author enters into various speculations as to 

 the formation and motion of auroral arches. Since it has been found 

 by experiment that the maximum length of the voltaic arc with a 

 given battery is nearly the same in atmospheric air and in highly 

 rarefied air, forming a very perfect vacuum, the author conceives 

 that a streamer begins as a disruptive discharge of finite and very 

 moderate length, (the maximum length very nearly of a continuous 

 discharge,) which starts upwards from the auroral arch, which he 

 regards as the discharging train. If this first portion be not parallel 

 to the dipping-needle, it is moved laterally by virtue of the earth s 

 magnetism, and thus wrenched, as it were, from the spot where it 

 was formed, and extinguished. If, however, the discharge, or any 

 portion of it, be parallel to the dipping-needle, it is not mfluenced 

 by the earth's magnetism, and remains. To this first length another 

 length may be added by a similar process, and so on, these successive 

 lengths being all parallel to the direction of the first, since otherwise 

 the streamer would be torn asunder by the lateral motion resulting 

 from the earth's magnetism. Thus a straight streamer extends up- 

 wards in a direction parallel to the dipping-needle. 



If, from some increase in the power of conduction of the arch, the ' 

 base'of the streamer be not necessarily confined to a single spot, then 

 a streamer may be formed which is somewhat inclined to the dipping- 

 needle ; but the consecutive elements of such a streamer must be in 

 the same direction, otherwise they would have different lateral 

 motions, the streamer would be divided, and the discharge would 

 cease. The streamer, as a whole, will move from east to west, or 

 from west to east, according to circumstances. Those streamers 

 which would tend to move north or south cannot exist, because 

 their bases would be severed from the auroral arch. 



If the discharge take place in air not so very highly rarefied, so 

 that the disruptive discharge is not quite of its maximum length, 

 consecutive elements need not be quite in the same direction m order 

 that the streamer may be unbroken, and thus curved streamers may 

 be formed. It is stated by M. Biot that such have sometimes been 



The author then enters into some speculations as to the nature of 

 the auroral arch, which he conceives to consist of nebulous matter 

 highly charged with electricity, and accounts, according to his views, 

 for tlie motion of such arches from the pole towards the equator. 



The remainder of the paper is occupied with speculations as to the 

 nature of fire-ball lightning, and other subjects relating to ordinary 

 electricity. 



