appears to subsist between it and the Formation of Clouds, 23 



6. Height of the Aurora. 



• 



Although I have taken very many observations with a view to 

 the determination of this point, yet from the want of comparable 

 notes, a satisfactory result has only in one instance (that of the 

 auroral arch of March 22, 1841) been attained. This arch was 

 observed at Durham by Prof. Chevallier, at York by Prof. Phil- 

 lips, and at Belfast by Prof. Stavelly. From the comparison of 

 the York and Durham observations, Prof. Chevallier deduced a 

 height of 156*6 miles, and from that of Belfast and York 157*3 

 miles. From a subsequent comparison with Prof. Chevallier of 

 his observations at Durham with mine at Dunse, the height of 

 the arch appeared to be about 160 miles. The close agreement 

 of these results is (when the nature of the subject is considered) 

 very satisfactory. 



From observations made by Mr. Brown, at Arbroath, and by 

 myself here, on the aurora of February 11, 1842, I deduced a 

 height of 63 miles above the earth's surface ; but from the im- 

 perfect definition of the auroral mass observed on this occasion, 

 there is considerable uncertainty as to the correctness of this 

 result, though probably not far from the truth. 



I need scarcely add my confirmatory testimony with regard to 

 the relation of auroral phenomena to the magnetic meridian, &c, 

 and their connexion with w magnetic storms," — points now most 

 satisfactorily established. 



II. Cirri. 



The following table is a summary of the directions of the 

 motions of cirri, from 1840 to 1847 inclusive : — 



For the sake of comparison with the above, the following table, 

 showing the directions of the winds at the surface for the same 

 years, is subjoined : — 



