Page:Journal of the Royal Geographical Society of London, Volume 1 (2nd edition).djvu/240

212 the aurora generally began in the W.N.W. and passed over to the N.E. until a certain period, after which it as regularly commenced in the N.E. and passed to the N.W.; whilst in 1827 the appearances of the meteor were as uncertain as the season was boisterous and changeable. The period when this change in the course of the light took place coincided very nearly with that of the equinox. The meteor was uniform in making its appearance always in the northern hemisphere, and generally in the form of elliptical arches from 3° to 7° of altitude, nearly parallel with the magnetic equator. The arches, when formed, in general remained nearly stationary, and gave out coruscatious, which streamed towards the zenith. These observations agree with those of Mr. Dalton, who always found a similar coincidence when the arches were complete. The light was decidedly seen between a fleecy, cloud-like substance and the earth. The proofs of this meteor belonging to the regions of our atmosphere were strengthened by different appearances of the meteor, and may be considered as completely established by the observations of Captains Franklin and Parry. The aurora was never attended by any noise, nor was any disturbance of the needle observed. It must be remarked, that Kater's compass was the only instrument observed, and then on board the ship only. Mr. Collie, the surgeon of the Blossom, has advanced an ingenious hypothesis on the nature of the aurora. It is probable that the new discoveries which are daily enriching science in electro-magnetism will remove many of the doubts which prevail on the nature and origin of this interesting meteor.

The Barometrical observations include researches on the horary oscillations, and on the mean altitude of the column of mercury at different parallels. The instrument used was an iron cistern marine barometer, of Jones's make: neutral point, 30.102; capacity, $1⁄24$; temperature, 52. It was suspended in Captain Beechey's tore cabin, and, with the exception of the first five months, registered every three hours. The diurnal variations are thus also contained in these researches. It has been supposed, that while the irregular oscillations appear almost null at the equator, and increase in extent towards the poles, the regular oscillations would appear to follow a contrary law, and diminish in extent towards the poles. The extent of the vibration of the column of mercury between the tropics was observed by Captain Beechey to be, in the North Atlantic, .038; in the South Atlantic, or between the equator and the tropic of Capricorn, to be .067; and the amount of the horary oscillations between both tropics was, for 3 − 026, for 9  + 019, noon + 011, 3  − 030, 9. + 014, and for midnight + 011. The mean vibration or extent from maximum to minimum, between the tropics, was, for the North Pacific, .059, and for the South Pacific,