50 AURORA. 



USE OF THE MAP.* 



1. To define the place and the extent of the aurora, the 

 observer should familiarize himself with the . relative position of 

 the stars in the northern sky, by frequent inspection of the ac- 

 companying map, or a celestial globe. 



2. Let the observer place the map before him, with the con- 

 stellations in the positions in which they actually appear at the 

 time of the observation. This may be done by holding up a 

 plumb-line between the eye and the pole star, noticing the stars 

 which it cuts; then a light pencil drawn through these stars and 

 the pole on the map will be the centre of the heavens, or place 

 of the meridian at the moment. 



3. Mark carefully the place among the stars of the arch of the 

 aurora, and show its width by parallel curved lines. Make a 

 note of the time. 



4. Draw a light curved line, following, as nearly as can be 

 judged, the outline of the arch down to the horizon, on each 

 side. 



5. If the arch changes its position, mark its new places at 

 intervals, noting the time of each observation. 



6. Letter each position A, B, C, &c., and note the time and 

 other particulars on the back or margin of the map, or in the 

 register. 



7. Beams or coruscations, or streamers of white or colored 

 light, may be marked by lines at right angles to the above, with 

 arrow heads pointing towards the place among the stars to 

 which they tend, or where they would meet, if prolonged. 



8. To aid in the estimation of angular distances the spaces 

 between certain conspicuous stars have been marked on the map, 

 which will furnish a scale to assist the eye, when actual measure- 

 ment may be impracticable. 



9. The course of brilliant meteors, when they fall within the 

 portion of the heavens included on the map, may be marked by a 

 line, the length of which will show the path of the meteor ; the 

 course should be indicated by an arrow, and the time recorded. 



The map, when filled, together with any written observations, 



* Copies of the map will be furnished by the Institution. 



