16 REPORT—1843. 
upon an axis, and by a multiplying wheel and pulley set it in rapid rotation; while 
rotating I made the magnetizing bars traverse from the equator of the globe to the 
poles. I then tested it with a proof needle, and found it to be regularly and perfectly 
magnetized. The next object was tc place this magnetic globe in similar electric 
circumstances to those which I conceived the earth to be in. Regarding that region 
of the atmosphere immediately over the torrid zone as the principal seat of atmo- 
spheric electricity, I conceived that if I surrounded the globe with a ring that would 
bear approximately the same proportion to the globe as this region of the atmosphere 
does to the earth, and electrized them oppositely, that the action of the electricity of 
the ring upon the air immediately enveloping the globe, would place the latter in 
nearly similar electric circumstances to those of the earth; if, then, the aurora were an 
electric phenomenon, that is, a discharge of free electricity, taking place from the pole 
of the earth, rendering the vortex, which I supposed to be immediately over the pole, 
luminous, from the great rarefaction of the air within it, and passing over our atmo- 
sphere to the upper stratum of the equatorial region, that as I could increase the elec- 
tric intensity of my artificial terrella as I pleased, an analogous effect would be pro- 
duced. This result followed with the greatest precision, as I shall now describe. I in- 
sulated the ring, and connected it with the resinous conductor of the rheo-electric 
machine. JI also insulated the globe, and connected one of its poles with the vitreous 
conductor, and placed it so that its equator was surrounded by the ring. These bodies 
being electrized differently, and at a very short distance from one another, one would 
expect that a discharge would have taken place between them; instead of this, they 
at once reacted upon one another, so that the exterior of the ring being resinous, the 
interior became vitreous; the equator of the globe resinous, and both its poles highly 
vitreous ; and a truly beautiful and luminous discharge took place from the uncon- 
nected pole, The state of the atmosphere has a remarkable effect upon the appear- 
ance of this discharge. One evening that the atmosphere was very dense, it had the 
appearance of a ring of light, the upper part of which was very brilliant, and the un- 
der part, towards the globe, was comparatively dark, just as we see at the bottom of 
ignited vapour; and indeed a vapour of some kind seemed to be ascending from the 
globe; above the ring, all round the axis, were foliated diverging flames, one behind 
the other. When the atmosphere is very dry it has merely the appearance of a bedu- 
tiful electric brush. Ifthe globe be moved towards any point of the interior of the 
ring, a discharge takes place in the line of shortest distance between them, and then 
there is a partial intermission of the auroral light. This experiment seems to point 
out the true cause of the aurora borealis.’”’ ‘The situation of the points of greatest 
intensity (commonly called poles) in magnets, he conceived to be merely a result of 
figure. Ona globular magnet the maximum intensity is, according to his experi- 
ments, situate about 75° from the equatorial zone. He maintained that the earth is 
a globular magnet, the maximum intensity of which is in lat. 75°, and that the mag- 
netic poles of the earth have never yet been found. Terrestrial magnetism being con- 
sidered as the effect of electric currents which move on the surface, will be affected 
by the irregularities of that surface, and hence the anomalies of the earth’s magnetism. 
The author denied the conclusiveness of the arguments used to show that the earth is 
an oblate spheroid. He asserted that globular magnets, if freely suspended, would, 
by their mutual attraction, rotate and revolve round each other; and, finally, that the 
doctrine of gravitation must ultimately give way to that of universal magnetism. 

On Determining the Index Error of a Circle by reflexion of the Wires of its 
Telescope. By the Rey. Dr. Ropinson. 
The observations made with an astronomical circle depend on an accurate deter- 
mination of its index error, for which various methods have been adopted, all more 
or less limited in applicability or deficient in accuracy. The method proposed in the 
present notice appears so convenient and accurate, that Dr. R. thinks it may be use- 
ful to lay before the Section a few details respecting its precision. Illuminate the lines 
in the focus of the telescope behind, so as to leave the field dark; the rays forming an 
image of them, emerge parallel from the object-glass, and if reflected from a mercury 
trough back into the telescope, will form an image of the lines, visible along with them. 

