102 



Fisher on the Variation of the Compass. 



The great irregularity in the results of these observations in 

 the course of a few hours is very remarkable, particularly the 

 three first, a difference occurring of about 3°, as no change of 

 circumstances at all affecting tlie needle ever took place in the 

 tent during the interval of these observations, and every possible 

 care was taken to remove iron from the place. The instrument 

 was likewise referred to the meridian mark, before and after each 

 observation. There likewise appears to be generally an increase 

 of atmospheric pressure corresponding to an increase of westerly 

 vaiiation. A similar analogy is likewise very apparent in the 



