The Aurora Borealis.—There have been seven exhibitions of the aurora borealis during the year 1849, two of which were sufficiently remarkable to merit something more than a passing notice.
The first occurred on the evening of January 14th. At 10 P.M., a well-defined auroral arch, about 5° in width, extended from NNE. to W., its highest part reaching nearly to Arided in Cygnus. At 11h there was one complete arch, and segments of two other arches, all brilliant, crossing each other in the NW., and throwing off intensely bright streamers, some of which reached the altitude of the Pointers. The aurora was now exceedingly beautiful, and emitted considerable light. The streamers appeared to have a duplex lateral motion, running along the upper edge of the arch from west to north, and then backwards from north to west. The clear sky beneath the arches was almost black, from contrast. At 11h 30m the arches had broken up, and the streamers appeared to emanate from the horizon.
February 18.—At 9 P.M. there was a brilliant band of auroral light in the east about 6° in width, which shot upwards towards the zenith, throwing off short lateral streamers. At times, a complete arch of varying width extended from the eastern to the western horizon; at others, it was broken up into two or more detached portions. At 9h 45m, a magnificent rainbow-like arch about 2° in width, spanned the heavens from ENE. to WSW. The altitude of the centre was apparently about 75°; the lower edge, at or near the highest point of the arch, was bounded by the star Castor. The arch was beautifully defined, and of perfectly even width throughout its entire extent; it disappeared in a few minutes after my attention was called to it, and soon after the sky became overcast. But for the absence of the moon, it might easily have been mistaken for a lunar rainbow. A precisely similar arch made its appearance here on the evening of the 21st of March 1833, and as far as my observation goes, these perfect rainbow-like arches are of exceedingly rare occurrence.
The following phenomenon though unconnected with auroræ, is probably of electric origin; and, as an unusual atmospheric appearance, is worthy of being placed on record:—September 16.—The sky was mostly overcast throughout the day, except a segment extending from WSW. to ENE., which was bright and clear to an altitude of about 15°. The upper boundary of the clear blue space was an elliptical segment formed by a sheet of white cloud, which was partially illuminated towards the western extremity, and somewhat resembled an auroral arch. I first noticed this blue arch about 3 P.M., and from that time until it disappeared, about six o'clock, there was not the slightest apparent change, either in its altitude or position. It was observed as early as 7 o'clock in the morning, when it was, nearer to the horizon.
General Remarks.—The year 1849 is the driest we have had since 1844; the fall of rain (39 inches) is 7·9 inches under the average annual depth, which is 47 inches nearly. From some cause, the annual quantity of rain at this place is evidently on the decrease, and the diminution is, I believe, general all over the north of England. Probably the large amount of moor and waste marshy land brought into cultivation of late years, and the more efficient drainage of the country generally, by diminishing the evaporating surface, and so interfering with that invisible process of nature which is the source of every kind of atmospheric deposition, may have led to this and other changes which appear to have occurred in the climate of England within the last half century. In the first seven years (1833-39) after I began to keep a meteorological record, the average annual depth of rain was 49·93 inches, or 50 inches nearly; in the last seven years, ending with 1848, the average is reduced to 43·74 inches. The greatest quantity in the last 17 years is 59 inches, in 1836; the least, 34·69 inches in 1842. The three driest years in the period are 1842, 1844, and 1849, which yielded 34·69 inches, 36·72 inches, and 39 inches.
The temperature of the past year (48°·69) is about half a degree below the climatic mean, which is 49°·02. The coldest year of the last 17 was 1845, and the mildest, 1846; the mean temperatures of these years were 47°·49 and 50°·85 respectively.
The naked thermometer on the grass, placed on raw wool, has been at or below the freezing point in every month of 1849; viz., in January, on 19 nights; in February, on 14; in March, on 13; in April, on 18; in May, on 11; in June, on 8; in July, on 1; in August, on 2; in September, on 5; in October, on 16; in November, on 13; and in December, on 24 nights. The amount of radiant heat thrown off from the earth's crust at night, in the year 1849, as indicated by naked thermometers placed on raw wool and on grass, is much greater than usual. The evaporation exceeds the fall of rain in five months of 1849; viz., in March, April, May, June, and September. In 1849, we have had 12 perfectly clear days; 163 days more or less cloudy but without rain; 190 wet days; 261 days on which the sun shone out; 33 days of frost; 13 of hail; 7 of snow; 10 of thunder and lightning; and 7 days in which lightning occurred without thunder. There have also been three lunar halos, one lunar rainbow, a double parhelion, and seven appearances of the aurora borealis.
The clear days are 14, the days of sunshine are 13, and the wet days are 8 less than the average number. The past year has therefore afforded a smaller share of blue sky and a less amount of sunshine than usual, although the depth of rain and the number of wet days are both below the average for the locality.
The quantity of electricity in the air was extremely small down to the end of July, after which it was restored to its average amount.
This fact is strikingly exhibited by the following table of continuous observations taken by M. Quetelet with Peltier's electrometer:—