488 THIRD REPORT 1833. 



servation should be ascertained from a map or otherwise. The 

 attention of observers is especially called to the point of ascer- 

 taining the time correctly, as it is one of the most important 

 points, and the one which probably will require the longest 

 forethought. 



4.) In default of intelligence of an Aurora, the observer 

 should go out of doors to some station where the horizon is 

 pretty clear, and look about every evening at 10, Greenwich 

 mean solar time, as near as may be. He should keep a journal, 

 noting for this time every evening whether there was an Aurora : 

 a single word will be sufficient. 



5.) As soon as the observer perceives or receives notice of 

 an Aurora, he should, if accustomed to magnetic observations, 

 observe the magnetic needle, and should go to some command- 

 ing situation with his watch in his hand, and a note-book. A 

 person so prepared will have little difficulty in fixing on the ap- 

 pearances most worthy of notice. We may, however, point 

 out the following : 



I. If there is an arch, the positions of its two boundaries, 



its terminations, &c., should be noted by the way in 

 which they pass among the stars, (the proportion of 

 distances between the stars admitting of very accu- 

 rate estimation by the eye). If, as rarely happens, 

 the sky is cloudy, the observer may notice the ele- 

 vation and extent of the arch, by moving till it appears 

 to touch the top of some terrestrial object, noting his 

 situation as well as he can, and the next day observing 

 with a theodolite the angular elevation and azimuth of 

 the object ; or ascertaining the height and horizontal 

 distance, and thence computing the angular elevation, 

 and observing the azimuth by a common compass : but 

 it is recommended not to adopt this method when the 

 observation of stars is practicable. Notice should be 

 taken whether one edge is better defined than the 

 other; whether there is a clear sky or dark cloud 

 above or below ; whether it terminates at the end in 

 sky or in cloud ; whether there is any dark band in 

 it ; whether in its general composition it is uniform or 

 striated ; whether stars can be seen through it, &c. 



II. If any change takes place in the situation or appear- 



ance of the arch, the observer should instantly look 

 at his watch and set down the time, and then proceed 

 to note the change. 



III. If there are beams or streamers, the time should be 

 noted ; then their position among the stars ; then their 



J 



