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V. On Periodical Laivs discoverable in the mean effects of the largei' Magnetic 
Disturbances. By Lieut. -Colonel Edward Sabine, R.A., Treas. ^ V.P.R.S. 
Received January 16, — Read February 27, 1851. 
In the preface to the first part of the first volume of the “ Observations on days of 
unusual Magnetic Disturbance at the British Colonial Observatories,” published in 
1843 , and in the introductory comments prefixed to the first volume of the “ Observa- 
tions at the Toronto Observatory,” published in 1845 , I stated the reasons which 
induced me to believe that the magnetic disturbances of large amount and occasional 
occurrence, designated in the Report of the Committee of Physics of the Royal So- 
ciety as the “ irregular variations,” and perhaps more commonly known by the name 
of magnetic storms or shocks, would be found, when studied in their mean effects on 
the local magnetic direction and force extending over a sufficient period of time, to 
have a character of periodicity, which if established, would leave no doubt as to the 
class of magnetic phenomena to which they should be considered to belong. The 
opinion thus expressed resulted from an examination to which I had subjected the 
series of two-hourly observations of the Declination in 1841 , made simultaneously at 
Toronto and at Hobarton, and those of 1842 at Toronto ; (the corresponding observa- 
tions for 1842 at Hobarton not having reached England in sufficient time to be in- 
cluded in the examination). Short as this period was, the evidence of the existence 
of laws of periodical action, connecting the effects of causes operating for the most 
part simultaneously at distant parts of the globe with the seasons of the year and 
the hours of the day at particular stations, was sufficiently systematic to induce me 
to regard this branch of inquiry as a most hopeful one, but as requiring for its pro- 
secution a longer continuance of observations than had been at that time provided 
for. At Toronto and the other observatories under the Ordnance Department, hourly 
observations were substituted in 1842 for the two-hourly series previously adopted. 
It had appeared desirable at the commencement of these establishments not to over- 
charge them with work ; but as it became obvious that whenever a physical theory 
should be brought forward to explain the phenomena which were the subjects of 
observation, such as, for example, those of the diurnal variation, there would be an 
immediate demand for the variation observed at least at every hour, arrangements 
were made, in the spirit of the Royal Society’s Instructions, to secure a better pro- 
vision for the requirements of theory than had been contemplated by the letter of those 
Instructions, and with this view observations at every hour were substituted for ob- 
servations at every two hours. The series at Hobarton (under the Admiralty) had 
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