during the Quarter ending December 31, 1848. 187 



from the 24th to the end of the month was 230 miles, the ex- 

 tremes being 300 miles and 70 miles; the average for the 

 month was 165 miles; 



From December 1 to 9 was 290 miles daily ; from the 9th 

 to the 15th was 170 miles ; and it was 94- miles from the 15th 

 to the end of the quarter. The extremes in December were 

 320 miles and 10 miles. The average for the month was 170 

 miles, and that for the quarter was 160 miles daily. 



In October the readings of the thermometer on grass were at 

 and below 32° on four nights ; between 32° and 40 ' on fourteen 

 and above 40° on thirteen nights. In November the lowest 

 reading was 21°*5 ; the readings were below 32° on eighteen 

 nights, and above 32° on thirteen nights. In December the 

 lowest reading was 18°, and the readings were below 32° on 

 twelve nights, between 32° and 40° on fifteen nights, and above 

 40° on four nights. 



The mean amount of clouds was 7*3 in October, and 6*7 both 

 in November and December. The averages for the seven pre- 

 ceding years were 6'9, 7*2, and 7*2 respectively. 



There were no less than twenty-four exhibitions of the 

 aurora borealis during the quarter ending December 31, 1848, 

 which occurred on October 18, 19, 20, 22, 24, 25, 27 and 80, 

 both in the morning and in the evening of the 30th ; Novem- 

 ber 13, 14, 17, 18, 21, 23, 24, 25, 26, 30; December 13, 17, 

 22, 27 and 29. At all these times the magnets were more or 

 less disturbed. In the weekly reports it was stated that from 

 October 1 7 to 30 the magnetic instruments were almost always 

 under some cause of disturbance, and particularly on the 17th, 

 18th, 19th, 23rd and 24th, slightly on the 21st and 22nd, and 

 moderate on the remaining days. The finest aurora was that 

 on the 17th of November ; this was best observed by Professor 

 Challis, and described by him in the Cambridge Chronicle. 

 The most important part of his communication was that rela- 

 tive to the varying position of the corona. Professor Challis 

 says, " I took twenty-four observations of the position of the 

 corona, partly by reference to stars, and partly by a small 

 altitude and azimuth instrument expressly constructed for this 

 kind of observation, which I call a meteoroscope. A compa- 

 rison of the results of the several observations seemed to show 

 that the central point has not a fixed altitude and azimuth, 

 but oscillates in a capricious manner about a medium posi- 

 tion, more especially in the azimuthal direction." Observa- 

 tions of this kind are of the highest importance for com- 

 parison with the varying positions of the corona with the 

 simultaneous variations of the magnetic dip and positions of 

 the magnets. "' 



