INTRODUCTION, 83 



The influences which this phenomenon may have on 

 the magnetic needle, as well as its connection with 

 the prevailing weather, are likewise to be attended 

 to. The long-since refuted notion, that a hissing 

 and crackling is heard in the northern lights, hardly 

 deserves to be mentioned. With respect to fire- 

 balls and falling stars, endeavour to mark, on a 

 celestial atlas, the place where such a meteor bursts 

 and disappears, and, when it can be done, its ap- 

 parent course ; from which, by means of the true 

 time, and the latitude of the place of observation, 

 the apparent elevation and azimuth may be de- 

 duced, and thence, combined perhaps with an ob- 

 servation made in another place, its distance from 

 the earth may be computed. 



These are, in general, the objects to which the 

 navigator has to direct his attention ; the methods 

 by which he has to observe them. For many ob- 

 servations the necessary conveniencLes will be 

 wanting, and, on the other hand, many phenomena 

 will occur, which are here either passed over, or 

 but slightly touched upon. The navigator's own 

 zeal for enquiry must do the most j his own know- 

 ledge, his inventiveness, and a laudable endeavour 

 to make all his efforts useful to the sciences, will 

 be better guides to him than any instructions. 



HORNER. 

 Zurich, 20th June, 1815. 



G 2 



