IN THE MEAN EFFECTS OF THE LARGER MAGNETIC DISTURBANCES. 139 
Although conclusions which are drawn from hourly observations, continued 
during three years at two stations, scarcely seem to require the support they may 
receive from their agreement with inferences previously drawn resting on a much 
narrower basis, yet it may not be unimportant to recall those, derived from a similar 
investigation to the present into the two-hourly observations at Toronto in the years 
1841 and 1842, which were published by me in 1845 in the Comments on the 
Observations of those years contained in the first volume of the Toronto Observa- 
tory. After remarking that the deflections produced by the disturbances are of 
sufficient magnitude and regularity of occurrence to constitute a recognizable and 
systematic component part of the mean diurnal variation obtained from observations 
of a month’s continuance or more, I stated as follows : “ By their easterly maximum at 
10 p.M. (together with the increasing prevalence of easterly deflections at the previous 
hours of 6 and 8), there is superinduced an excess of easterly direction at those hours, 
which appears to be in great measure the cause of the westerly retrogression of the 
magnet at the succeeding hours of midnight and 2 a.m. ; and we are thus led to infer 
the probability, that if the whole effect of the disturbing cause, or causes, could be 
eliminated, the residual portion of the diurnal variation might appear as a single pro- 
gression with but one maximum and one minimum in the twenty-four hours. 
“ The conneetion which thus appears between the systematic operation of the dis- 
turbances and the occurrence of a double progression in the diurnal variation, would 
lead to an important inference in regard to the disturbances themselves, to which it 
may be well to advert, in order that the subject may receive further examination by 
the observations of other observatories. The hours of the night at which the otherwise 
continuous easterly march of the diurnal variation is interrupted, appear to be the 
same, or very nearly the same, at all the observatories at which results have yet been 
published. If this interruption be either wholly, or in great measure, occasioned by 
the influence of the disturbances, operating in a systematic manner, as they are found 
to do at Toronto, the deflections which they produce at other stations must also have 
a similar systematic character, and be connected, as those of Toronto are, with the 
hour of the day at the particular station. 
“We should in such case arrive at the important conclusion, that whilst the dis- 
turbances must be attributed to general causes, inasmuch as they are found to prevail 
on the same days in different and very remote parts of the globe — it must also be re- 
cognized, that their operation, in every particular locality, is regulated by a law which 
respects the hours of the place.” 
The investigation, which has been the object of this paper, is obviously incomplete 
until a similar examination shall have been made of the influence of the larger dis- 
turbances on the mean diurnal variation of the Inclination and of the total Force. I 
may perhaps hope to make such an investigation the subject of a future communica- 
tion. 
