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VIII. On Periodical Laws discoverable in the mean effects of the larger Magnetic 
Disturbances. — No. II. By Colonel Edward Sabine, R.A., Treas. and V.P.R.S. 
Received March 18,- — Read May 6 , 1852. 
In a former paper presented to the Royal Society in January 1851, bearing- the same 
title as the present, I submitted to the Society the evidence afforded by the principal 
disturbances of the Magnetic Declination at Toronto and Hobarton in the years 1843, 
1844 and 1845, of the existence of periodical laws by which their occurrence and 
mean effects appeared to be regulated. At the close of that paper I expressed the 
intention of submitting, on some future occasion, the results of a similar investigation 
into the periodical laws which might be expected to show themselves in like manner 
in the disturbances of the other two magnetic elements, viz. the Inclination and the 
Total Force. 
Having since had occasion to examine the disturbances of the Declination at the 
same two stations in the three succeeding years 1846, 1847 and 1848, I have had the 
satisfaction of finding that the observations of these years confirm every deduction 
which I had ventured to make from the analysis of the disturbances of the former 
period ; whilst new and important features have presented themselves in the compa- 
rison of the frequency and amount of the disturbances in diffei'ent years, apparently^ 
indicating the existence of a periodical variation, which, either from a causal con- 
nection (meaning thereby their being possibly joint effects of a common cause), or by 
a singular coincidence, corresponds precisely both in period and epoch, with the 
variation in the frequency and magnitude of the solar spots, recently announced by 
M. ScHWABE as the result of his systematic and long-continued observations. As 
facts and collocations of this description are of particular interest at the present 
moment, from their bearing on inquiries in which physical philosophers are engaged, 
I have deemed it better to communicate them at once, in the form of a second paper 
on the disturbances of the Declination, than to await the completion of the investiga- 
tion into the laws of the disturbances of the Inclination and of the Total Force, for 
which I have not yet been able to command the necessary leisure. 
The method pursued in examining the laws of the Declination-disturbances in 1846, 
1847 and 1848, is the same as that adopted for the three preceding years and described 
in my former paper. The observations having been made hourly, every hourly ob- 
servation which was found to differ by a certain prescribed amount^ from the mean 
value of the Declination in the same month and at the same hour was separated from 
* Philosophical Transactions, Part I, 1851, p. 127. 
