Mr William Sturgeon on the Aurora Borealis. 231 



and at the point of contact, — circumstances I'equired by the hypothe- 

 sis ; or, in other woi'ds, there are but very few magnetic meridians 

 in this curve of equal variation, that run sufficiently close to the 

 north-western magnetic pole of the earth, to satisfy the conditions 

 of the hypothesis. In Great Britain, and throughout the northern 

 parts of the curve, the magnetic meridians pass north of the pole ; 

 and the magnetic meridian, for the same curve, opposite the coast of 

 Spitzbergen, would pass the magnetic pole northward upwards of 

 10° of latitude. Westward, over the Atlantic Ocean, the magnetic 

 meridians of this curve would approach the north magnetic pole 

 more closely ; and in Newfoundland, the magnetic meridians would 

 probably pass through that pole ; but on the American Continent, 

 towards Hudson's Bay, the magnetic meridians would pass the north- 

 western pole, some 3° or 4° on its south side. 



I have selected this paiticular curve of equal vai'iation, as it 

 stands in Professor Barlow's map, because it is that which passes 

 through the north of England, and corresponds with the variation 

 at Kendal (25°), when Dr Dalton made his observations. Had the 

 selection been made on the curve of 20°, which passes through the 

 most western parts of Spitzbergen, through Norway, France, Al- 

 giers, and the Canary Islands, thence across the Atlantic to Nova 

 Scotia, Canada, and Hudson's Bay, the deviations of the magnetic 

 meridians from the magnetic pole would have been much greater, 

 especially in Europe, where the meridians have been more exactly 

 ascertained than in any other pai't of the curve, — that is, through 

 the whole of the curve from the Mediterranean to Spitzbergen ; in 

 which the magnetic meridians would cross the meridian in which 

 the north-western magnetic pole is situated on its northern side, and 

 the magnetic meridian of Spitzbergen would cross the meridian of 

 the pole 15° or more north of it. In the western portion of the 

 curve, however, from Algiers to Hudson's Bay, the magnetic meri- 

 dians would run sufficiently close upon the magnetic pole to answer 

 the conditions of the hypothesis. But the deviation of the western 

 line of no variation, from the meridian of the magnetic pole, would 

 alone be sufficient evidence of the incorrectness of the hypothesis. 



In all these cases, the north-western magnetic pole is supposed to 

 be situated in 69° 53' north latitude, and 93° 33' west longitude, 

 as calculated for the year 1800, which is the nearest date on record 

 to 1793, the year in which Dr Dalton first published his theoretical 

 views of the aurora borealis, and which are those that still appear in 

 his last edition, published in 1836. 



In referring again to that part of the hypothesis which places the 

 auroral beams " parallel to each other," and at the same time, " pa- 

 rallel to the dipping needle at the places over which they appear," 

 it is obvious, that, to fulfil these conditions, the dipping needle would 

 have to assume one and the same position, both in dip and direction, 

 at all places over which the auroral beams appear at any one time ; 



