XXIII. Calculations of the Heights of the AurortB Boreales, of the nth September 

 and 12th October, 1833; with Observations upon the Locality of the Meteor. 

 By Richard Potter, M.A., late Fellow of Queens" College, Cambridge, 

 and Professor of Natural Philosophy and Astronomy, University College, 

 London. 



[Read December 8, 1845.] 



The data I have employed for the calculations of the heights of the arches of the Aurorae 

 Boreales, which were seen on the nights of September 17th and October 12th, 1833, are chiefly 

 contained in the Conspectuses of the observations printed and distributed, together with various 

 recommendations, to members of the British Association for the advancement of Science. 



In one instance, additional information is used from the Yorkshire Gazette; where Mr. 

 Phillips gave the breadth of an arch which he had omitted in the Conspectus. 



In consequence of the attention of scientific men having been drawn to the subject, the 

 observations on these displays of the Aurora Borealis, were much moi-e complete than had ever 

 l)een obtained before. The time in the various observations was reduced to Greenwich time, 

 by Mr. Phillips the Secretary of the Association, which thus facilitates the comparison of the 

 phenomena noted by different observers : nevertheless they have never before been carefully 

 discussed. The partial discussion communicated by Professor Airy to this Society in November 

 1833, and published in the Philosophical Magazine for December of that year, is the only 

 previous discussion of them, that I am aware of; and the height was investigated only by 

 a graphical method, which appears to have given results very inaccurate for many of the 

 observations. 



Regular observations on the Aurora of September 17th were taken by Mr. J. Phillips at 

 York, by Mr. Clare, Mr. Hadfield and myself, at or near Manchester, by Professor Airy, at 

 Cambridge, and by the Hon. C. Harris, near Gosport. 



On the 12th October, regular observations were obtained by Professor Sedgwick, at Dent, 

 near Sedbergh, by Mr. W. L. Wharton, near Guisborough, by Mr. J. Phillips, at York, by 

 Mr. Clare, Mr. Hadfield and myself, at or near Manchester, by Dr. Robinson, at Armagh, by 

 Professor Airy, at Cambridge, and by the Hon. Charles Harris, at Heron Court, near Christ- 

 church, Hants. 



The arches being perpendicular (or very nearly so) to the magnetic meridians of the places 

 of observations, a base for trigonometical calculation is more certainly obtained with respect to 

 them, than any other parts of the appearances. In the following calculations, 1 have accordingly 

 used observations on the arches only. 



In the Conspectus for the 17th September, I find only two sets of contemporaneous obser- 

 vations, the one for Cambridge and Manchester, at 8*'. 25"" Greenwich time; the other for York 

 and Gosport, at ll''.0"'. Manchester and York are too nearly of the same magnetic latitude 

 to furnish an adequate base. To these I may add an observation of ray own, of the altitude 

 of an arch and its extent on the horizon, for calculating the height from an observation at 

 one place only, by means of a subsidiary hypothesis that the arches are portions of small circles 

 round the magnetic axis. 



