Height of the Auroral Arch of March 20, 1865. 377 



the people, and ifc is hoped that when a road is finished 

 between Thonon and Morzine, they will have niore useful 

 occupation, and come into greater contact with persons more 

 reasonable than themselves. 



HEIGHT OF THE AURORAL ARCH OF MARCH 20, 



1865. 



BY A. S. HEESCHEL, B.A. 



Since the laws of meteorology have become better known, and the 

 practice of recording meteorological observations more widely 

 extended, the appearance of the aurora has attracted attention, 

 more particularly in its connection with the local variations 

 of the magnetic needle. When the aurora is observed from 

 different points of view, it is important to note especially the 

 moments when individual phases of its principal features occur, 

 which may afterwards be connected with the motions of the 

 magnetic needle. A connection should be established with 

 the daily telegraphic signals, to identify the time with Green- 

 wich, Edinburgh, or Dublin, at the first of which observa- 

 tories self-registered photographs of the movements of the 

 magnetic needles are recorded continuously, and are capable 

 of being compared afterwards with observations of auroras, 

 when these have been referred to standard Greenwich time. 



On the 20th of March last, at 8h. 20m. p.m. G. M. T., an 

 auroral arch at Manchester was observed by Mr. Baxendell, 

 spanning the zenith from west to east, which about twenty 

 minutes later had changed its position very sensibly, the 

 western portion having moved in a southerly, and the eastern 

 portion in a northerly direction. At the same time an exten- 

 sive magnetic disturbance was observed, the index of a 

 delicate instrument constructed by Dr. Joule for showing, 

 rapidly, minute changes of magnetic declination being driven 

 entirely out of the field of view. At Hawkhurst the luminous 

 arch was first observed at G. M. T. 7h. 50m. p.m. It dis- 

 appeared completely at 8h. 30m. p.m. During this short 

 space of time the curves of the magnetometers at Greenwich 

 show that the needle moved eastwards, and back again, 

 through nearly half a degree of an arc of a circle. In a ver- 

 tical sense, the needles remained nearly unaffected or oscillated 

 in a less degree (see Fig. 1). Such an effect upon the mag- 

 netometers would be produced by a galvanic current, at the 

 summit of the atmosphere, flowing from north to south, over 



