DESIDERATA, ETC. 
XXXV11 
should be ascertained from a map or otherwise. The attention 
of observers is especially called to the point of ascertaining 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, ob¬ 
serve the magnetic needle, and should go to some commanding 
situation with his watch in his hand, and a note-book. A per¬ 
son 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 accurate 
estimation by the eye). If, as rarely happens, the sky 
is cloudy, the observer may notice the elevation 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 di¬ 
stance, 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 clear sky or dark cloud above 
or below ; whether it terminates at the end in sky or in 
cloud 5 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 
height among the stars ; their motion (whether verti- 
