4. Brilliant auroras were generally succeeded by bad weather. Those on the other hand which did not rise to any great height in the sky, or which did not show any special mobility, were regarded as the precursors of calms. None of the theories which have been ventilated are in exact accordance with all the manifestations of these northern lights. The undulating motion of their waves of light, their rolling forth like pillars of smoke driven by winds, has hitherto remained unexplained. Although electrical processes, still unknown, seem to be the main causes of the Aurora, atmospheric vapours may, however, have a considerable part in producing the phenomenon; and nothing so much favours this supposition as the indefinite form in which it often appears. Its occurrence during the day, _i.e._ light clouds with its characteristic movement, has been rather imagined than actually observed. The transition of white clouds into auroral forms at night has never at least been satisfactorily proved. Falling stars pass through the northern lights without producing any perceptible effect, or undergoing any change. A dirty sulphur yellow was characteristic of all auroras when the sky was overcast with mists or when they were seen by moonlight. In clear weather they were colourless. [Illustration: THE AURORA DURING THE ICE PRESSURE.] 5. Their influence on the magnetic needle was very variable. While the quiescent and regular arches had little or no effect, the quicker and more fitful streamers, especially when accompanied with prismatic colours, produced great disturbance in it. Sir John Ross remarked, that the aurora when tinged with deep red colour had a great effect on it, although he completely stultifies his observation by his supposition, that the phenomenon was produced by rays of the sun reflected on the vast fields of snow and ice surrounding the Pole. Parry in 1820 could discover no effect from it either on the magnetic needle or on the electrometer. During the winter of 1872-3, the character of the northern lights was much altered, though their colour remained constant. At first they consisted chiefly of bands of light, running from the south-northwards. At a later period of that winter they assumed for the most part the appearance of coronæ, and then their direction was from the north southwards. During the voyage of the _Tegetthoff_ the observations of the behaviour of these lights and of the magnetic constants were taken by Weyprecht, Brosch, and Orel by means of a magnetic theodolite, a dipping needle, and three variation instruments. The extraordinary disturbances of the needle rendered the determination of exact mean values for the magnetic constants impossible. The diminution of their intensity was considerable during the continuance of auroras. In 79° 51′ N. Lat. and 58° 56′ E. Long. the declination amounted to 19½° E. and the inclination to 82° 22′. The ice-pressures which occurred in December, 1873 together