Brilliant white clouds seen.
About midnight the sky was almost clear, but south were two or three brilliant light clouds, colour very white-yellow, shape cumulo-stratus. From about west to near south extended a long feathery light of the same colour, parallel with the horizon, and between south and west there appeared occasionally brilliant small clouds. The upper edges seemed hairy, and gave one the idea of a bright light behind a cloud. The forms changed, but no particular order was noticed.
(Here follows a description of the spectrum, and the mode in which a delineation by the lines was obtained.)
March 6, 1874. Capt. Maclear suggests whether a low barometer has to do with the absence of red.
(4.) At 8 P.M., March 6th, 1874. This was a slight Aurora, seen to the southward; after this the clouds changed to high cirrus. Capt. Maclear suggests whether a low barometer has any thing to do with the absence of red in the spectrum, the normal state of the barometer being an inch lower in those regions than in more temperate latitudes.
Barometer falls after the Aurora, and strong gale from the S. or S.W. follows.
Edin. Encyc. vol. iii. article “Aurora.” Dr. Kirwan observed that the barometer commonly falls after the Aurora. Mr. Winn, in the seventy-third volume of the Phil. Trans., makes the same remark, and says that in twenty-three instances, without fail, a strong gale from the south or south-west followed the appearance of an Aurora. If the Aurora were bright, the gale came on within twenty-four hours, but was of no long continuance; if the light was faint and dull, the gale was less violent, longer in coming, and longer in duration.
Pale yellow glow rare in the Aurora Borealis.
The pale yellow-coloured glow referred to by Capt. Maclear is, in my experience, rare in the Aurora Borealis. It is probably the “æqualiter et sine eruptionibus aut radiis fulvi,” described by Seneca (antè, p. 1), and may probably belong to more southern climes.
Spectrum of Auroræ Australes extends more into the violet.