Magnetic Declination. 



353 



or 6^ P.M. in June is only half a minute (0''5) ; about this hour, also, the numbers of positive differences and 

 negative differences are nearly equal ; and since the mean of the observations at G*" p.m. in June is within half 

 a minute of the monthly mean of all the observations, the probable eiTor of a single observation in June 1 844 

 at 6"^ P.M. would be only about 0''5 from the mean declination for the month : a degree of accuracy which is 

 quite equal to any thing that can be expected from a month's observations with the best portable apparatus. 



TABLE XX. — Number of Positive and Negative Differences which occur between the limits of 

 successive Minutes for each Hour in 1844. 



MAG. AND MET. OBS. 1844. 



4n 



