418 Mr. Dalton on the Height of the Aurora 



table for occultations of stars, is a table which contains the 

 time in which the moon is above, and the sun below the 

 horizon. 



The times of rising and setting of both these heavenly bodies 

 being placed opposite to each other, this is likewise only copy- 

 ing of numbers. 



A third auxiliary table contains the stars which within the 

 largest possible limits may be occulted. For this purpose I 

 sought for the beginning, middle, and end of the year, the de- 

 clination which the moon has for every 5° of right ascension, 

 and took in all the stars which are 40' further north, and 

 1° 40' further south, than the northernmost and southernmost 

 limits of those zones. 



By means of these tables the decision of the possibility of 

 an occultation is in general so much facilitated, that besides 

 the 130 occultations given in the book, only two were calcu- 

 lated in which the moon remained distant somewhat more than 

 2', the limit to which I had proposed to myself to find out the 

 conjunctions. 



LXIX. On the Height of the Aurora Borealis above the Sur- 

 face of the Earth ; particularly one seen on the 29th of March, 

 1826. By John Dalton, F.R.S.* 



A PPREHENDING that the Royal Society will favourably 

 •*•*' receive accounts that have a direct tendency to determine 

 the height of that interesting phenomenon, the Aurora bore- 

 alis, I have been induced to transmit some observations that 

 were made upon a very remarkable one, which appeared in 

 the evening of the 29th of March, 1826. From some recent 

 observations, an opinion seems to be entertained by some 

 writers, that the aurora is not so high as has generally been 

 estimated ; but it is only from facts and observations such as 

 the following, I conceive, that any near approximation to the 

 true height can be obtained. 



The aurora borealis above mentioned, was of a kind very 

 rarely occurring. It assumed the appearance of a rainbow- 

 like arch, stretching across the mid-heaven, at right angles to 

 the magnetic meridian. It was subject to very little change 

 of position for an hour or more, and therefore afforded time 

 to observe the angle of its elevation above the horizon. In the 

 period of five years' observations at Kendal formerly, above 

 one hundred appearances of the aurora occurred to me, and 



* From the Philosophical Transactions for 1828. Part II. 



only 



