1837.] 



Dip and Intensity at Madras. 



223 



No. 3, not marked. 

 h. m. s. 



April 26th 20o 0' 85.2 i 343 6-1 1 ^ 



12 30 101 48 17.1 J 311,0 i 9 t 3l ?\'? 



9 0 201 53 27.5 310.4 ) cor. for temp. 1.31 



309.39 



April 30th 20 0 87.8 1 1 25 17.3 > ., 10 T > „„ RA 



11 45 101 30 29.4^ 312 - 1 f 31150 



7 30 — - 201 35 40.7 311.3 f P ' 



4 0 87.3 301 40 51.8 311.1 ) cor. for temp. 1.40 



310.10 



or we have for the time of performing 100 vibrations at the tempera- 

 ture of 60° Fahrenheit at Madras. 



Needle 3, x Needle 3. 



s. s. 



300.14 309.39 



.17 310.10 

 .59 



Mean, 300.30 Mean, 309.74 



If k and h' represent the magnetic intensities at any two places, 

 and T and T' the times of performing 100 vibrations at those places, 

 then we have 



*.-(*)■ 



applying this, the horizontal magnetic intensity for Madras (that at 

 London being assumed = 1.) becomes 



s. 



By Needle No. 3, x 2,1738 



Ditto ditto No. 3, 2,2245 

 With a view to compare theory with practice, we might now com- 

 pute the number of oscillations which No. 3 x ought to make at 

 Madras from the observed number in London ; thus, assuming the 

 Dip for London to be 69<> 10' N. the formula becomes 



I 3 -f- sec. 2 (69° 10') * § : | 3 -f sec. 2 (60 52' 30") £ § : : 462776^ 2 : T 2 



performing the computation T = 344,87 differing to the amount of 

 44,57 seconds from the observations. This difference between theory 

 and observation, is but one of many instances which have from time to 

 time occurred in the infant state of a science. Observation has led us 

 to a theory, and then again has shewn the incompleteness of such 

 theory. In the case of Magnetism, we have long since been prepared 

 to expect that local causes might considerably interfere with its esta- 



