LIEUT. -GENEEAL SABINE ON TEERESTEIAL MAGNETISM. 



465 



following Table, the face of the circle being directed towards the east, which was its 

 customary position in observations at sea. 



Table V. 



The weights and deflections obsei"ved on shore at Simon's Bay, Cape of Good Hope, 

 in April 1843, with the face of the circle towards the east, were as follows: — 



Table VI. 



Hence we have the magnetic force at Simon's Bay, as derived from the needle 

 of the 'Erebus' at Hobarton 13-540 X :4^||=7-585 ; and from the needle of the 

 'Terror' at Hobarton 13-540 X ;|i°f-^ = 7-539. The mean between these values is 

 7-562. The force at the anchorage of the 'Erebus' and 'Terror' corresponding to 

 the mean epoch of 1842.5, derived from the absolute determinations at the magnetic 

 observatory at the Cape of Good Hope (page 458), is 7-574. 



The small difference in amount between the values derived from the absolute determi- 

 nations at the Cape Observatory (including the correction to Simon's Bay), and that 

 assigned from the Hobarton Observatory by the needles of the ' Erebus' and ' Terror,' is 

 well within the limits of the errors of observation and of deduction ; and gives full 

 reason to infer that the magnetism of the needles underwent no material alteration in 

 the interval. 



Deduction of the Magnetic Force at the land stations visited intermediately between 

 Hobarton in April 1841 and Simon's Bay in April 1843. 

 In this deduction we have the advantage that the deflections by the weights were 



