OF THE AURORiE BOREALES. ETC. 323 



We have here one of the rare cases which fix the identity of the phenomenon seen ; the arch 

 appearing double at places so distant as Cambridge and York at the same time. 



The distance of the projections of York and Cambridge on the magnetic meridian whose 

 variation is 24°. SO' is 129.97 miles. The altitude of -y Ursse Majoris at York at 7^. 56"°^. 

 was 22°. 50'; therefore the altitude of the summit of the arch was 19°. 50'. 



The altitude of 7 Ursas Majoris at Cambridge at 7*. 54". was 21°. 3'; consequently the altitude 

 of the highest point of the arch was 10°. 31-^'. 



These data give the summit of the arch 199-93 miles distant from York, and its height 

 above the earth's surface 72.2 miles. 



From Mr. W. L. Wharton's observations at Guisborough. 



" 8^. 20". — Well defined arch, passing between a and /3 Ursfe Majoris its summit somewhat 

 above ^ Ursas Majoris, no radiations." 



From the Hon. Charles Harris's observations at Heron Court, 4 miles N.W. of Christchurcli, 

 Hants. 



" S*". 22". — Bright, irregular arch, like a luminous bank of fog, about 8° above the horizon." 



The distance of the projections of Guisborough and Heron Court on the magnetic meridian 

 whose variation is 24°. 30' is 225.1 miles. 



The altitude of ^ Ursa9 Majoris at Guisborough at 8'\ 20". was 28°. 47'; therefore the summit 

 of the arch would have an altitude of about 29°. The breadth of the arch passing between 

 « and /3 Ursae Majoris would be 5° ; therefore the altitude of the lower edge would be 24°. 



In the Hon. Mr. Harris's observation we have the altitude of tlie lower edge 8° - refraction 

 = 7°- 53'. 



From these data we find the distance from Guisborough to have been 167.34 miles, and the 

 height of the under edge to have been 70.9 miles. The breadth being 14.6 miles, the height 

 of the upper edge was 85.5 miles. 



From the observations of Professor Sedgwick at Dent, near Sedbergh, Yorkshire. 



" s"". 55". — The upper part of the arch, better defined than before, passed between a and /3 

 Ursae Maj. and very near ^ Ursae Maj. Its vertex in or near the magnetic meridian. &c." 



From my own observation near Manchester. 



" 8*'. 53^'". — The arch has its vertex under ^ Ursae Maj. and its upper edge touches y 

 Ursae Maj., altitude about 19°. 30'." 



At 8*'. .'54". Mr. Hadfield found, near Manchester, but on the opposite side, that the altitude 

 was 20°, and the extent on the horizon 120°. 



The distance of the projections of Dent and Manchester on the magnetic meridian with 

 variation 25°. 30' is 52.56 miles. 



The altitude of ^ Ursae Majoris at Dent at s''. 55"'. was 26°. 32', therefore the altitude of the 

 arch passing near it we may call 26°. 26'. Mr. Hadfield's observation corrected for refraction 

 gives the altitude at 8\ 54". as 19°. 57'. 



With these data we find the arch to have been 183.38 miles from Dent, and the height of 

 the upper edge to have been 84.97 miles. 



The arch, or rather arches, appear to have been stationary from about 8''. 54". to 9''. 10"., 

 for from Profes.sor Sedgwick's observations we have, 



"9''. 10". — Arch nearly as before." 



From Mr. Clare's observations at Manchester, who has recorded the arch as double at 8^. 54"., 

 we have 



" 9''. 9". — The two arches remain in the same position." 



From Dr. Robinson's observations at Armagh. 



"9''. 1". — Three parallel arches, the principal one has its upper edge on Polaris, and midway 

 between Capella and fi Auriga; ; its lower a little above /3 and y Ursa; Majoris. 



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