1S3^] Terredi ioJ Magnetic Force hi Southern India. 27 i 



tlie granitic form;i}ions (here met (llie Saclras hills), bat if so, 



Paljuncottah and Nagracoi! (at which places similar hut larger onuses 

 for disturbance exist) oug];t to shew the same-, whereas they exhibit a 

 very small, but opj-nsile, teiitlencVe Or it would appear on the wliole, 

 tiuil {lie diatnbuficn of magnetic infensitg in Southern India h' tuit liitlc 

 1711 erf red ivi til bg local causes , and, with reference to Madras, that the 

 Iccutiun chosen for rniikiug the observations exliibits an intensity in ex- 

 cess, to the amount of 1,0098 to 1. 



Assuming this, wo will now con-.pare the magnetic intensity of Madras, 

 and of the magnetic equator wilh tliat of London; for which purpose 

 we have the following observations made with the two hitensity cylin- 

 ders belonging to Captain D. Bethune, already adverted to at the ccni- 

 niencement of this paper. The observations in Lcndon were, I pre- 

 .sume, made by Captain Bethune, whereas those at Tvladras in 1837 were 

 nrade by Capt. B. and myself conjointly, and those in IS3D by myself 

 alone. 



Mean i'me orcvpi d Ci;-''in I r.' No. o X rnid Ke.'^ hi manhig \Q, 

 vibrat'iom, at the temperature of ('.0°. 



at Madras. in London. 



No. 3 X No. 3 No. 3 X No. 3 



6" S 



442.76 461.9G 



s s 

 300.30 309.7-1 



.. 303.2G 310.83 



Date. 

 In the year 1835 



1837. 



April 30 1 

 May 3)" * 



1839. 



Jan. 29 . . . 



A mere glance at these numbers, shews that one, if not both of the 

 cylinders, had diminished its intensity at the lime of making the first ob- 

 servations at ^ladras; and that after tvventy-one months (v/hen the 

 second observations were made) they iiad still further diminished their 

 intensities No. 3 X, by 2.9Qs and No. 3, by 1.00^; hence it would appear 

 pro!)able that in 1835, when the London observations were made, these 

 cylinders, with their then stronger intensities, at Madras would have 

 performed 100 vibrations in something like 294.s' and 307.^ respectively : 



as the numbers now stand (recollecting that-^—^~^ ' ; and putting 



A — i for the horizontal intensity of London) 



