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VI. On Periodical Laws in the larger Magnetic Disturbances. 
By Captain C. W. Younghusband, Royal Artillery, F.R.S. 
Received February 16, 1853, — Read February 24, 1853. 
Having submitted the hourly observations of the magnetic declination made at 
the St. Helena and the Cape of Good Hope Observatories to a course of examination 
similar to that undertaken by Colonel Sabine for Toronto and Hobarton, and 
published by him in the Philosophical Transactions, Part I. for 1851, and Part I. for 
1852, also in Vol. II. Magnetical and Meteorological Observations at Hobarton, and 
Vol. II. Magnetical and Meteorological Observations at Toronto (now in the press), 
with the object of investigating some of the laws which govern the occurrence of the 
larger magnetic disturbances, I have found that at these two stations, as well as at 
the two others, the evidence is complete of the existence of laws of a periodical 
character : the facts appear to be important materials towards elucidating the general 
laws of disturbances, and I therefore venture to communicate them to the Royal 
Society. 
The observations which have been examined are comprised between September 
1842 and September 1847 at St. Helena, and between July 1841 and July 1846 at 
the Cape of Good Hope; these periods include all the hourly observations that could 
be made available for discussion. 
The observations were made simultaneously at all the magnetic stations, viz. at 
the commencement of each Gottingen hour ; we have, therefore, the best opportunity 
of judging of the degree in which the disturbances may be referred to one general 
cause, while by arranging them with regard to local time, the means are afforded of 
showing the operation of laws which have respect to the sun’s position towards the 
place, both in relation to the hour of the day and the season of the year. 
At St. Helena, every observation that differed by 2‘5 scale divisions from its normal 
place (meaning by that, the mean place at the hour, and in the month in which the 
observation occurs) has been regarded as a disturbed observation, and separated 
from the others ; the number of observations thus separated amounts to 2659 ; the 
whole number of hourly observations made in the period amounted to 36,054, 
wherefore one observation in 13’6 has been regarded as disturbed. At the Cape, in 
like manner, every observation that differed by more than 2‘5 scale divisions has 
been regarded as disturbed and separated from the others ; the number of separated 
observations is 3038, the number of hourly observations made in the period is 36,571s 
wherefore one observation in every 12‘0 is disturbed. 
MDCCCLIII. 2 
