Appendix. 313 
terrestrial magnetism, and on the other hand is dependent on certain 
changes in the envelope of the sun, the nature of which is as yet 
little known. At Cape Adare, which is probably within the circle 
of the greatest Aurora intensity in the Southern Hemisphere, 
particularly favourable opportunities are afforded for its study. 
During the cold months the atmospheric conditions are most favour- 
able, the amount of cloud being small. During the winter the 
phenomenon was observed nearly every night, so it was possible to 
establish the diurnal period, for it usually manifested itself between 
6 P.M. and 3 A.M., its maximum intensity being generally reached 
between 8 and 9 р.м. Of course there were exceptional cases. 
The intensity also appears to be greater at the time of the equinoxes 
than during the mid-winter months; the displays being more 
brillant and more rapid in motion at the former time. ‘They were, 
however, most frequently seen during July and August. At Cape 
Adare (lat. 71? 18' o" S.) the Aurora was always observed in the 
north, and it always manifested itself in exactly the same manner. 
Diffused Aurora light would first appeai in the north about 3° above 
the horizon; soon afterwards a gigantic luminous arc would form 
above the diffused Aurora, the extremities resting on the horizon, 
while the apex was situated a little to the west of the magnetic 
meridian. | 
The luminous arc generally formed the starting-point for the 
. radiant draperies of rays, of variegated colours and with indescribably 
beautiful and graceful folds, which moved laterally and most rapidly 
from E. to W., and bodily across the zenith. Long shafts of light 
would shoot down towards the earth with incredible rapidity, the 
colour being of a much deeper red at the lower part of these 
shafts than at the upper. The intensity of the colour appears to 
have some connection with the altitude of the phenomenon, varying 
greatly with the density of the atmosphere. In other words, the 
colour of the Aurora beams is an indication of its height above 
the surface of the earth, being deep red at a low altitude, and of a 
pale nebulous whiteness at great altitudes. But what was of greatest 
interest in the observation of the Aurora was the connection which 
appeared to exist between it and an approaching atmospheric 
disturbance ; a strong gale from the S.E. being almost invariably 
preceded by a most brilliant and rapid Aurora display. This was 
not a mere coincidence, but a fact repeatedly observed. It was 
also possible to predict an approaching storm many hours beforehand 
by the extreme agitation of the magnetic needle, both possibly being 
manifestations of the same cause. 
