880 Royal Society, 



end of the magnet towards the east and towards the west, and the 

 effect of each considered separately. 



The periodical character of disturbances at St. Helena and the 

 Cape in a cycle of years is indicated insofar as the limited extent of the 

 observations would permit ; sufficient however to point to the year 

 1843 as that of least disturbance at these two places, by showing a 

 regular decrease from the previous years, and an increase in every 

 succeeding year of observation. Though the hourly observations 

 were discontinued before 1848, the year which Colonel Sabine has 

 shown to be that of periodical maximum, as 1843 was that of mini- 

 mum magnetic activity at Toronto and Hobarton, the observations 

 now discussed are shown to be quite consistent with this period, and 

 thus tend to establish it as a general law of magnetic phenomena. 

 In the aggregate of each year the disturbances towards the west are 

 shown to preponderate over those towards the east, both at St. 

 Helena and the Cape of Good Hope ; a similar preponderance of 

 westerly over easterly has been found in every year of observation 

 at Hobarton, but at Toronto the easterly disturbances exceeded the 

 westerly both in number and amount in every year. 



Arranging the disturbances into the several months of their oc- 

 currence, the greatest disturbance is found to occur in January 

 and the least in June at St. Helena and the Cape of Good Hope ; 

 the same months being those of greatest and least disturbance at 

 Hobarton, whereas at Toronto, 5oM January and June are months of 

 minimum disturbance, the maxima disturbance occurring there in 

 April and September. 



From this identity of the epoch of greatest and least disturbance, 

 — at St. Helena, where the months of January and June are not 

 those of opposite seasons, viewed either with respect to the sun's ex- 

 treme altitude or to extreme periods of temperature, — at the Cape, 

 situated in S. latitude 33° 56', — and at Hobarton in S. latitude 

 42° 52', — and contrasting this identity with a different law at To- 

 ronto in N. latitude 43° 39', the author infers that the principal 

 causes which produce an annual period of disturbance are not de- 

 pendent upon local seasons. It is likewise pointed out that about 

 the period of the equinoxes there is a tendency to maximum dis- 

 turbances at all the stations, producing absolute maxima at Toronto, 

 faintly but systematically indicated at the other stations. 



The westerly disturbances were found to exceed the easterly in 

 every month in the year at St. Helena and the Cape, which agrees 

 with the results deduced from the Hobarton observations, while it 

 appears from the observations at Toronto that the easterly disturb- 

 ances exceeded the westerly in every month. The average value of 

 a westerly disturbance is greater than that of an easterly in every 

 month at St. Helena and the Cape of Good Hope. The disturbances 

 at Hobarton again coincide with this result ; and in a slight and less 

 perfectly marked degree, Toronto has the same peculiarity. 



Arranging the disturbances into the several hours of their occur- 

 rence, the hours of the day are found to be those of greatest disturb- 

 ance in a very considerable degree ; the sum of the ratios, during 

 the twelve hours of the day, being about seven times as great as the 



