[Sidenote: M. Silbermann’s observations, 15th April, 1869. Cirrus clouds took the place of the Aurora.] In the Encyc. Brit. edition 9, article “Aurora Polaris,” after referring to the evidence of Franklin, Richardson, and Low, M. Silbermann (‘Comptes Rendus,’ lxviii. p. 1051) is quoted in detail for observed connexion between the Aurora and cirrus cloud. 15th April, 1869, at 11h 16m, an Aurora appeared and disappeared; but it seemed as if the columns were still visible, and it soon became obvious that fan-like cirrus clouds, with their point of divergence in the north, had taken the place of the Aurora. Between 1 and 2 A.M. the clouds had passed the zenith, and let fall a little fine frozen rain. At 4 A.M. the cirrus of the false Aurora was still visible, but deformed towards the top, and presenting a flaky aspect. The cirrus never appeared to replace the Aurora either from right or left, but to substitute itself for it like the changes of a dioramic view. [Sidenote: Payer thinks the transition of Aurora into clouds not proved.] Payer, in his ‘Austrian Arctic Voyages,’ thinks that the occurrence of the Aurora during the day (i. e. _light clouds with its characteristic movement_) had been rather imagined than actually observed, and that the transition of white clouds into auroral forms at night has never been satisfactorily proved. He, however, mentions the mist-like appearance of the Aurora. [Sidenote: Dr. Allnatt’s observations, 4th February, 1872, at Frant. Aurora passed into cirro-stratus.] Dr. Allnatt observed the splendid Aurora of 4th February, 1872, at Frant, and noticed the weird and wonderful appearance of the phenomena. At 6 P.M. the Aurora commenced by the S.W. portion of the heavens being tinged with a bright carmine hue, and in a short time the whole visible hemisphere was lighted up. A dark elliptical cloud extending from S. to S.E. and S.W. sent up volumes of coloured radii. At 7 the Aurora had passed the zenith, and a dark, broken, rugged cloud some 8° E. of zenith was surrounded by electric light of all hues. At 7.40 the Aurora began to wane, and passed into a homogeneous cirro-stratus of sufficient density to obscure the stars, disappearing at 7.45. [Sidenote: Later, cirro-stratus was transformed into luminous cumulus.] At a later hour of the night the canopy of cirro-stratus had separated and was transformed into luminous masses of radiant cumulus; so that, as Dr. Allnatt observes, there were called in requisition almost all the most prominent cloud-modifications during the progress of the phenomena. The succession of formation, transformation, and reformation from Aurora to cloud and from cloud to Aurora was, Dr. Allnatt concluded, conclusive of the theory before advanced of the electric origin of the recurrent rayed cloud-modifications in the place of the magnetic meridian, over which so much mystery had been cast. _Aurora and Thunder-storms._ [Sidenote: Aurora and thunder-storms. Silbermann’s theory.]