Height of the Auroral Arch of March 20, 1865. 379 



proposed by Fisher and (many years later) by De la Rive. 

 Whether the principle of stratified discharges is adequate or 

 insufficient to explain these great " semi- great- circles " that 

 pass in succession over our heads, must be left to magnetolo- 

 gists to decide ; for whenever there is aurora there is infallibly 

 large magnetic disturbance. 



Shortly after, or simultaneously with the disappearance of 

 the arch, a luminous glow appeared upon the north-west 

 horizon at Hawkhurst, Burton, Manchester, and other places ; 

 which continued from 8h. 40m. p.m. to 9h. 25m. p.m., and 

 then gave place to a display of auroral streamers, observed at 

 Burton- on- Trent and Windermere. This part of the display 



Pig. 2. Change of Position in an Auroral Arch, March 20th, 1865. 



appears to have been too distant to affect the magnetometers 

 at Greenwich. 



It is important to note particularly the position in the 

 heavens occupied by the luminous arch (or other principal 

 portions) of an aurora at any time and place, as it is by a 

 comparison of these with other observations of a similar 

 nature recorded elsewhere that the distance of the meteor 

 from the earth can be calculated. The luminous arc observed 

 at Hawkhurst, from 7h. 50m. p.m., to 8h. 30m. p.m., on the 

 20th of March, appeared as a narrow, well defined band of 



