TRANSACTIONS OP THE SECTIONS. 7 
iitiosabtres. When a single conductor bounded by segments of two epberic^ 
■fitts Mtting at an angle which is a submultiple of two right angles is electrified 
r^kinfluenLf a charged body, the effect may be represented by means of afimte 
Ler of images disposA in a symmetrical manner m the circumference of a circle 
the exciting body, and cutting the two sphenca surfaces at nght 
Jla The principle of electrical images, as applied 
Sraed by a reference to the successive images of » 
jnliel plaM mirrors, and to the symmetrically arranged images which are seen m 
k hIckJoscope. _ 
SmBestdtsofa new Calcvintien of tJie PertiirhaHons of Uranus hy the 
Planet Nq)tunc. By J. C. Adams, M,A,y /'./i-A.o. 
%&eEpghlof Auroral Arches. By the Rov.Prof.CnEVALLiEB, F.R.A.S. 
Of 1)1 the pbrnnomeua of the aurora borealU, the arcliw -f 
• amir at right angles to tlie magnetic meridian we the most 
■sat. uil seem to offer the most promising means of ^ Xumlrer of 
VBin which that modification of the aurora i« formed^. In the U . 
^iftiJ«phic*l Transactions. IV. Dalton haa collected several 
Bt. aid arrives aX the conclusion tliat these arches about 100 mUes mfeh. 
H computed the height of three such arches, 1 am d«iJoas ^>'‘“8 J®* 
^iinefly before the AsBodation. The first was Uio aurora^ March 22. 1841, 
■••tfvedMDunse. near Berwick, by Mr. William Stevenson ; ’ 
SBelfm, by Mr. SteveUy ; ami at York, by Mr. Dbilbps., ' .uh * oaS. 
^ fwmore than an hour, from S'* 50'" Greenwich mean time to 10 ; Md the posi 
'»o«( the arch was definitely fixed by its place among tlw fixed stars. The direcnoa 
jiiardiwaa mogoetically east and west: Its height was . rjnrbnm • 
i^oWrvations at York and Durham, York and Belfast and Belfast a*»d 
i««aifiagaUiiudes being 156, 157, and 166 miles The 
JtrvedouSept.21. 1846, at Esh. ncai' Durham, by raysell, and at Norw oy 
Manilill. it was visible only for about five minutes. Ihe 
* l«C nlk». ThU determination depends upon two observations only. 1 he tmr 
•"iltfch was seen on the lOth of March 1S47. It was observed nt 
in Linculushire. at Cambridge, at No^icb. m ' d 
aud Leeuwardea in Holland. The observations of 
from a base of 172 miles, give aii altitude of , f 1nes. 
ud Cambridge, from a base of 1 14 miles, give an allitu c 
(if Spalding and D-rlington, from a bn^* which 
^•I174'9 miles 5 the mean being 175 miles. TTie tnok nlacc at 
J observed is remarkable. A groat magnetic dixlurbaucc took place a 
^ time, extending as far as Toronto. I« comiexirm with the cause tjrese 
it cannot eswpe notice that there U simdanty between,^^^^^^^ 
l^ of suforai action and the two modes of , jj.pctioa of the 
^Fvaday. the ordinary auroral beams being 
*'P«tt»l meridian, and the arches bc-ing at right angles to that direction. 
On a Graphical Method of computiny an Occul^on. 
%fAcJlev. Prof.CnEVALMER»/^-«‘^*'^; 
j^«m«bod is founded upon Bessel's mode of the centre 
'^y moon. The apparent place of a . Agpending upon 
expressed by two groups of . . .ug ^tber depend- 
moon with respect to the centre ae the first group 
the place of observation. Tiic nuontities simple formulmj 
for a time near the middle of the LcoU^ at Berlin, 
j, •already computed in tlie Berlin Ephemens from tables easily 
J^'j^eswhic!: compose the second group ^ EeSn^poch. in I 
Wtid for a given place, or may be computed expressly f 6 , ^ these 
^ wnple maimer. The differcudra of the cwresponding quanuties in eacn 
