IN THE LARGER MAGNETIC DISTURBANCES. 
169 
although a minimum of disturbance occurred at Toronto in midsummer, still the 
disturbances in the four summer months had a considerable preponderance over 
the disturbances in the four winter months ; at Hobarton also the disturbances 
in the four summer months greatly exceeded those in the four winter months, 
and it seemed reasonable to refer the maxima and minima periods of disturbance 
in their mean effects to extreme seasons ; St. Helena however offers a remarkable 
objection. The sun is vertical at St. Helena early in November, and again early 
in February, but there is no indication of the occurrence of the disturbances 
being connected with the sun’s position relative to the place. The temperature 
reaches its maximum in the middle of March, and its minimum early in September ; 
and if we consider the periods of extreme temperature to be those of extreme seasons 
at St. Helena, we shall find that at both those times the disturbances have their mean 
value, proving that insofar as St. Helena has extreme seasons, they are undoubtedly 
not coincident with extreme disturbances. While, therefore, we can class St. Helena, 
Cape of Good Hope and Hobarton together, places differing so widely in climate and 
geographical position, as exhibiting their maximum and minimum disturbance in the 
same months of the year contrasted with Toronto as presenting a different taw, we 
may conclude that the principal causes which operate in producing the annual 
variation of the disturbances are not dependent upon local seasons. 
There is, however, a striking point of similarity at all the stations about the times 
of the sun’s passing the equator. At Toronto, April and September are both months 
of maxima disturbance in the year, September being that of primary maxiinuin. At 
St. Helena a distinct tendency towards maxima is shown in the same two months, 
rather more strongly marked in April than in September. At the Cape of Good Hope 
the tendency towards maxima in the same two months is also quite apparent, but 
still more strongly marked in April over September than at St. Helena. At Hobarton 
the tendency to maxima in April and September is likewise evident, though not so 
marked, and here, as at Toronto, September’s maximum preponderates over that of 
April. 
The average value of a single disturbance scarcely differs in any of the months, 
either at St. Helena or the Cape ; at Toronto and Hobarton the average value of one 
disturbance appears to be least in their summer months, about a mean in winter, and 
greatest in the equinoctial months. 
Table V. contains the ratios of the numbers and values of the westerly to the 
easterly disturbances in the different months. The westerly disturbances exceed the 
easterly in every case ; the preponderance has its greatest excess in the month of 
May, and its least in the month of February at both stations. It also appears that 
the ratio of westerly values is greater than the ratio of westerly numbers. At 
Hobarton the westerly tendencies were also found to exceed the easterly in every 
month, while at Toronto the easterly exceeded the westerly in every month ; and it 
is worthy of remark, that at these two stations, as well as at the Cape and St. Helena, 
the ratios of values likewise exceeded the ratios of numbers', the amount in every 
instance is small, but decided. 
