The ordinary colour of aurora is white, usually with a distinct yellow tint in the brighter forms, but silvery white when the light is faint.
Sometimes a Holtz machine was employed, but even without it illumination resembling aurora was seen on several occasions, extending apparently to a considerable height.
The calculated heights - all referring to the lowest border of the aurora - varied from o 6 to 67.8 km.
Such display as that of the aurora borealis.
On some of these occasions aurora was brilliant in both the northern and southern hemispheres, whilst magnetic disturbances were experienced the whole world over.
If, as is now generally believed, aurora represents some form of electrical discharge, it is only reasonable to suppose that the auroral lines arise from atmospheric gases.
Relations to Magnetic Storms. - That there is an intimate connexion between aurora when visible in temperate latitudes and terrestrial magnetism is hardly open to doubt.
Gives particulars of the number of occasions when aurora was seen at each hour of the twenty-four during three expeditions in high latitudes when a special outlook was kept.
In high latitudes for several months in summer it is never dark, and consequently a total absence of visible aurora is practically inevitable.
The first settlement in the vicinity of Aurora was made in 1834.