AND ANNUAL VARIATION OF THE TERRESTRIAL MAGNETIC FORCE. 215 
Although I have been unwilling to encumber this communication with details from 
the Hobarton Observatory similar to those from Toronto, I may be permitted to 
state very briefly the results obtained at Hobarton in respect to the annual variation 
of the Inclination and Force, as they have a very considerable interest when viewed 
in connection with those obtained at Toronto. 
A series of monthly determinations of the inclination, in which no change was 
made in the instruments employed, or in the methods or place of observation, was 
commenced at Hobarton in June 1843, and was still continuing at the date of the 
last returns received from thence in December 1848. From this series we have sixty- 
eight consecutive monthly determinations, strictly intercomparable, bearing on the 
question of annual variation. It will be remembered that the summer of the southern 
hemisphere is when the sun is in the southern signs, and vice versa ; and that at 
Hobarton it is the south end of the needle which dips below the horizon. The in- 
vestigation, conducted in the same manner as at Toronto, shows at Hobarton a de- 
crease of south inclination of 0'‘89 on the average of the months from April to August 
inclusive, i. e. in the southern winter ; and an increase of 0'‘85 from October to 
February inclusive, ^. e. in the southern summer. Thus in the months from April to 
August the North Inclination at Toronto and the South Inclination at Hobarton are 
both diminished ; and from October to February inclusive they are both increased. 
The North Inclination at Toronto is lowest and the South Inclination at Flobarton 
highest, in the respective summers of the two stations, and vice versd, and in both 
cases the variation is nearly to the same amount. 
In the case of the horizontal force, a regular and consecutive series of monthly de- 
terminations, similar to that at Toronto, was commenced at Hobarton in January 
1846, and the results have been received in England to December 1848 inclusive. 
The series treated in a similar manner to that at Toronto shows an annual variation 
of the same character as respects the seasons, and almost identical in amount with 
that at Toronto. In the months from October to February inclusive (or in the 
summer months at Hobarton), the horizontal force is ‘0017 greater on the average 
than its mean amount, and from April to August inclusive (or in the winter months 
at Hobarton), it is on the average 'OOIS less than its mean amount. 
The inferences to be drawn from these variations of the inclination and horizontal 
force taken conjointly, as respects the total force at Hobarton, are as follows : the 
inclination being greater from October to February than from April to August, if the 
total force remained unaltered, the horizontal force should be helow its mean amount 
in the months from October to February, whereas we find a higher amount in those 
months; therefore, so far as the observations have yet gone, the total force at 
Hobarton appears to be subject to an annual variation, being higher than its mean 
amount from October to February, and lower than its mean amount from April to 
August. 
It may assist the recollection of the facts regarding the annual variation of the two 
