636 
LIEUT.-COLONEL SABINE ON THE ANNUAL VARIATION OF THE 
each hour, irrespective of the Diurnal Variation, or the changes which the mean de- 
clination undergoes at different hours. The hours are those of mean solar time at 
each station, the day commencing at noon, and being reckoned through the twenty- 
four hours; noon is therefore =0'*. The fractional minutes are occasioned by the 
observations having been made at the exact hours of Gottingen time, which differ 
more or less at each station from exact hours of local time. 
The Annual Variations represented in Plate XXVI. were obtained at Toronto from 
three years of observation, viz. 1845, 1846 and 1847 ; at Hobarton from five years, 
viz. July 2, 1843 to July 1, 1848 ; at the Cape of Good Hope from five years, viz. July 
2, 1841 to July 1, 1846 ; and at St. Helena from three years, viz. from July 2, 1844 
to July 1, 1847. The secular change at the several stations during the years of ob- 
servation has been eliminated ; but what are frequently called the “ irregular disturb- 
ances,” are retained, as all observations are taken into the account. At Hobarton, 
the Cape of Good Hope and St. Helena, the Annual Variation is probably very little 
affected by the disturbances referred to ; but it may be otherwise at Toronto, where 
they are larger, and especially influential during the hours of the night when the 
regular range of the Annual Variation is small. It is not probable, however, that the 
annual range during the hours of the day is materially affected by the disturbances, 
even at Toronto. The absolute values of the magnetic elements at the respective 
stations were nearly as follows in the mean of the years in which the observations 
were made : — 
Toronto. 
Hobarton. 
Cape of 
Good Hope. 
St. Helena. 
Declination 
Inclination 
Total Force 
Horizontal Force 
Vertical Force 
1°33' W. 
75° 15' 
13-90 
3-54 
13-45 
9° 57' E. 
— 70° 34' 
13-56 
4-51 
12-78 
29° 07' W. 
-53° 25' 
7-48 
4-46 
6-01 
23° 51' W. 
-22° 07' 
6-01 
5-57 
2-26 
As the mode in which the subject of the Annual Variation is treated in this com- 
munication is I believe in some respects new, it has been suggested to me, since 
this paper was presented to the Society, that a fuller description than is given in 
the preceding paragraphs, of the process by which the graphical representation in 
Plate XXVI. is derived from the actual observations, may be desirable. I have 
therefore subjoined in Plate XXVII. a graphical representation for two of the 
stations, Toronto and Hobarton, of the direct and immediate results of the observa- 
tions themselves, exhibiting according to their absolute declination-values the mean 
declination in each of the twelve months, at each of the twenty-four hours, of a mean 
year. The observations thus represented are, as before stated, at Toronto, three 
years of hourly observation, from January 1, 1845 to December 31, 1847 inclusive; 
and at Hobarton five years of hourly observation, from July 2, 1843 to July 1, 1848 
inclusive. The mean or middle year at Toronto is therefore from January 1 to 
