IN THE MEAN EFFECTS OF THE LARGER MAGNETIC DISTURBANCES. 129 
Whence we perceive, that whether we regard the separate account of the easterly 
or of the westerly disturbances, we find the numbers increase from a minimum in 
January to a maximum in April, and decrease to a second minimum in June; that 
they then commence afresh to increase to a maximum in September, and thence de- 
crease to the minimum in January. With the exception of a small excess of easterly 
disturbances in July in comparison with August, the progression, which has been 
found to take place when the combined easterly and westerly disturbances were under 
consideration, is found to be the same when the separate portions are examined. 
The minima of each progression are in January and June ; the maxima in April and 
September. 
Distinct from this is the conclusion we may obtain if we make an intercomparison 
of the numbers in the respective columns of easterly and westerly disturbances. By 
this intercomparison we are led to perceive that in November, December and January, 
the number of westerly disturbances exceeds the number of easterly ; that in the adja- 
cent months on either side, viz. in October and February, the number of each is 
nearly equal ; and that in all the other months of the year the easterly disturbances 
predominate; the predominance being greatest in June and July. Thus we observe 
that the causes which produce large easterly deflections of the north end of the mag- 
net, when compared with those which produce westerly deflections, are most in- 
fluential in June and July, and least so in December and January, Hence, it happens, 
that the June minimum of westerly disturbance is less than the January minimum, 
and is the minimum of the year in that portion of the disturbed observations ; whilst 
the January minimum is less than the June minimum of easterly disturbance, and is 
the minimum of the year in that portion. We find also in the excess of easterly dis- 
turbances in June and July, a probable explanation of the small apparent irregularity 
already noticed in the progression of the monthly numbers in the easterly disturb- 
anees, wherein a small excess appears in the July numbers in comparison with those 
of August. The excess in the total number of disturbed observations in the summer 
quarter over the winter quarter, appears also to be due to the excess of easterly dis- 
turbances occurring in the summer quarter ; for if we regard only the westerly dis- 
turbances, we find their numbers to be even somewhat greater in winter than in sum- 
mer (westerly disturbances, November to February, 160 : May to July, 150 : easterly 
disturbances, November to February, 127 : May to July, 240). 
If we now pass to the distribution of the 1650 disturbed observations into the re- 
spective hours of their occurrence, and seek in the numerical relations which may be 
thus manifested the evidence which they may atford of the existence of a diurnal 
affeetion, we may in the first instance examine the number of disturbed observations 
occurring in each of the hours, independently of the question of whether they are 
easterly or westerly disturbances : they are as follows : — 
MDCCCLI. 
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