1839] 



Terrestrial Magneile Force in Southern India. 



227 



not more accordant tlmn those already obtained from the other needles. 

 Notwithstanding this, Yn. Caldeooft, at some considerable inconvenience 

 to himself, repeated his observations with the new needle at Cochin and 

 AUepee, previously to his departure for Europe. I have thought it ne- 

 cessary to mention th-^se particulars, in order to arconnt for havhig so 

 long delayed fulfilling mv promise of giving these observations : but mv 

 desire to render the work complete, eve7i now makes it vo htf l , / I had 

 not better wait for the observations on the ivesferyi coast ; but, with thus 

 much by wav of apology, and the promise that, at some future, not far 

 distant time, the observations on the western coast will be completed; 

 we may at once turn to the observations, and their discussion : and, since 

 there will be much to say in the way of discussion, it may be as well to 

 leave the intensity observations for the present, and commence the 



Discussion of the Dip Observations. 



The discordant results which have been met with by Captain Sabine* 

 and others in measuring the dip by different instruments, renders it de- 

 sirable that a comparison of the needles now used with others should 

 be instituted ; accordingly I have availed myself of two observations 

 made here with a dip apparatus belonging to Captain Drinkwater Bethune 

 R. N., and of three observations made with Mr. Caldecott's needles— 

 we get altogether as follows : — 



Dip for Madras. 



o / // o / /; 



Needle D. B. No. I from 1 observation ^ 

 D. B. „ 2 1 



T. G.T. „ 1 2 . 



T. G. T. „ 2 1 ■ 



T. G. T. „ 3 2 



T. G. T. „ 4 I 



J. C. „ 1 1 



. J. C. „ 2 2 . 



Mean 



The discrepancies here met with, probably for the most part arise from 

 error of observation ; since only one or two results from each needle have 



= + 6 55 4 ? 



= 6 49 56 f 



= 6 45 22 



= 6 44 13 I 



= 6 56 56 { 



= 6 54 4 J 



= 6 51 34 > 



= 6 53 26^ 



= 6 51 19 



-h6 52 30 



-i-6 50 9 



-1-6 52 30 



* In the observations lately made for the magnetic survey of Ireland, there appears, in 

 an extreme case, a difference of 41' between the results from two of the needles em^ 

 ployed. 



