33® Mr. Christie's theory of the 
in each month great irregularities, attributed by Canton to the 
effect of the aurora borealis, are observable ; and in deducing 
the mean times of maximum and minimum variation, I have 
excluded all the observations on the days on which these 
irregularities happened. These are however few, and I am 
not aware that including them would have much affected the 
results ; but as my object is to determine the more regular 
effects, I consider that, in taking the mean, they are better 
excluded. Canton's observations were not always made at 
corresponding hours on different days ; so that, to obtain the 
mean variation at or near to particular hours, I have taken the 
observations nearest to such hours, on the several days in 
each month ; and taken a mean of the times, and of the 
observed variations. The following table contains the results 
thus deduced. 
