180 Scientific Intelligence — Meteorology. 



were seen at this epoch, an inferior limit, notably higher than 

 the result of the observations of Franklin and his companions. 

 The particulars of its colouring have also been noted with care, 

 and the results may be thus stated. The usual colour is a yel- 

 lowish tint, which may become whitish or greyish, especially to- 

 wards the conclusion of the phenomenon. The more striking ex- 

 hibitions of colour are produced by red tints or green ; and these 

 are witnessed only in the most beautiful auroras, which occur, in com- 

 parison to the others, in the proportion of one to five. This kind 

 of colouring seems to require, as a condition, great vivacity of 

 splendour, and very rapid undulatory movements or vibrations. 

 The mode of the distribution of the colours has also been studied, 

 and is very remarkable. When an arch is very brilliant in a clear 

 sky, it forms at the lower part a light reddish shade, and at the 

 upper a very slight greenish tint, and the general shining light con- 

 tinues imprisoned between the two small coloured zones ; ere long 

 the rays appear ; but this phenomenon, upon the whole, is far from 

 common. Even when the vibratory movement is perceptible, if 

 there be any shooting of the rays, the red tint occupies the base of 

 the ray, the green the summit, and the yellow the intermediate 

 space. In proportion as the splendour increases, the more the co- 

 lours at the extremity extend, and at the expense of the colour be- 

 tween them. If the splendour diminishes, these colours retreat to 

 the extremities of the rays, and then disappear. If, on the other 

 hand, the ray is following an undulatory motion, and is moving 

 along parallel to itself, of the two lateral faces one exhibits the red 

 tint, and this is the anterior one, whilst the other and posterior one 

 is of a green hue.' These two tints have not at all appeared iden- 

 tical with their homonyms of the solar spectrum. Possibly the red 

 aurora of our climates may be explained by the appearance of arcs 

 or rays, whose lower part alone is visible to us. Three or four 

 times the aurora borealis has been seen, apparently placed between 

 the observer, on the one hand, and the clouds or the mountain snow 

 on the other. 



The influence of the aurora borealis upon the magnetic needle 

 has been studied with the greatest care : that of the more brilliant 

 ones was very conspicuous; the needle almost always traversed to- 

 wards the west, then returned to its point of equilibrium, and ad- 

 vanced towards the east, and did not definitively return to its ori- 

 ginal position, till after a series of oscillatory movements which 

 were usually very irregular. The maximum deviation observed has 

 been 4^ 30', and this on the evening of the 22d of February ; and 

 it is especially during the appearance of coronas that these striking 



