The Geissler tubes represent the upper part of the atmosphere which becomes luminous when the Aurora Borealis is observed in the northern hemisphere. The phenomena produced by the Lemström apparatus are considered consistent with the theory advocated by Swedish observers that electrical currents emanating from the earth and penetrating into the upper regions produce Auroræ in both hemispheres. The experiment differs from the apparatus of M. de la Rive, who placed his current _in vacuo_, and did not show the property of ordinary atmospheric air, in allowing to pass unobserved, at the pressure of 760 millims., a stream of electricity which illuminates a rarefied atmosphere. [Sidenote: M. de la Rive’s apparatus described.] De la Rive’s apparatus was also exhibited at the same time, and will be found described at p. 385 of the Catalogue, No. 1749. A large sphere of wood represented the earth, and iron cylinders the two extremities of the terrestrial magnetic axis. These penetrated into two globes filled with rarefied air, simulating the higher regions of the Polar atmosphere. The electric discharge turned around a point situate in the prolongation of the axis, in a different direction at either pole, when the two cylinders were charged by means of a horseshoe electro-magnet, in accordance with observations on the rotation of the rays of the Aurora. [Sidenote: De la Rive’s magnet in an electric egg.] De la Rive placed an electro-magnet in an electric egg. As soon as the magnet was set in action the discharge which had before filled the egg was concentrated into a defined band of light, which rotated steadily round the magnet. [Sidenote: Gassiot’s experiment with 400 Grove cells and exhausted receiver between poles of magnet.] Gassiot describes an experiment with his great Grove’s battery of 400 cells, in which an exhausted receiver was placed between the poles of the large electro-magnet of the Royal Institution. “On now exciting the magnet with a battery of 10 cells, effulgent strata were drawn out from the positive pole, and passed along the under or upper surface of the receiver according to the direction of the current. “On making the circuit of the magnet and breaking it immediately, the luminous strata rushed from the positive pole and then retreated, cloud following cloud with a deliberate motion, and appearing as if swallowed up by the positive electrode.” Mr. Marsh considered this bore a very considerable resemblance to the conduct of the auroral arches, which almost invariably drift slowly southward. [Sidenote: Mr. Marsh considered the Aurora an electric discharge between the magnetic poles of the earth.]