MAGNETIC FORCE IN IRELAND. 



195 



TABLE IV . (Continued.) 

 Observations of Dip and Intensity. Needle S (2) *. 



When the observations of dip made at the same station with 

 different needles are compared together, it will be found that they 

 are by no means in accordance. Thus the dip at Limerick in 

 November, 1833, deduced from four observations with a needle on 

 Meyer's principle, was 71 ll'-7, while the mean of five observations 

 with needle L (1) at the same place and in the following year was 

 only 70 59'-5, differing from the former by 12'. When from this 

 difference the amount of the annual change is deducted, the re- 

 mainder appears to be greater than can be fairly ascribed to the 

 errors of observation. But these discrepancies in the results given 

 by different needles have been placed in the strongest light by the 

 recent observations of Captain James Ross in London. In these 

 observations, which were undertaken with the view of determining 

 the amount of the annual decrease of dip at London, eight different 

 needles were employed, and from eight to ten observations were 

 made with each, the result of each separate observation being a 

 mean of eighty readings. 

 The results were as follow : 



Needle B (1), Admiralty, ... (10 obs.) 



Needle L (1), (9 obs.) 



Needle S (1), (8 obs.) 



dip 



69 r-5 



69 6-3 

 69 11-3 



* The observations in Limerick, July, 1835, made by Captains Sabine and Ross ; 

 ill the remaining observations with this needle by Captain Sabine. 



o2 



