1839] Terrestrial Magnetic Force in Southern India. 229 



of a very bad oLservatiun (one in wlii-h I bad purposely been careless), 

 and one which pioved very discordanr, to dis over, by ihrusiing the nee- 

 dle among sotne iron filii g'», viheie the po'es were sifuaied; when, my 

 discordant observation was fnUy expl iimd by the pole's having chosen 

 to take up a position at a and 6, forining an angle of 11 degrees with the 

 endse and e'. 



I now, for the sake of variety, in -Hn^d the mignefs a little, so as to 

 establish the poles at a' and 6', and, as might be expt^cted, ares.ilt difF^M-- 

 ing 3^ degrees from that just made, immediately resulted: the former 

 being as much in excess as the latter was in defect. 



I now set to work systematically— thus — at Trivandrum August 30th — 

 13th September l8J7. — 



Needle employed. Observed dip. Remarks. 



O / I' 



Needle No. 1 = — 3 17 30 T Each result being the mean of 5 observa" 



= .'"5 20 0 I tions in one position of the needle only; 



■ = 3 1:2 3 j made with the greatest possible care, that 



* = 322 3U V. 'he [)oles should be ^etiled at the ends e e\ 



f Ea( h derived fr 'm5 observations in the 

 — = — 4 7 G ^ -i ime p« siticm as above, by ca.jsing asiight 



*' — 4 7 0 1 legree of inclination in one of the magnets, 



( v\ hereby the poles were bi mated at e and a, 



f From the mean of 5 observations in the 

 same position as above, mri^n-tized by in- 

 clining both magnets siit^htiy, whereby the 

 poles took up the position b' and a. 

 r Eiich result being derived from 5 obser' 

 Needle No. 4 = 0 9.2 30 )v^''t)n« i" one position of the needle only, 



-j- 0 17 30 ^magnetized bv causing a sli:4ht inciinaiion 



( of both magnets, or poles at a' and 6. 



Q 37 30 C ^^ '^ resu't being derived from 5 obser- 



~ ' • ^ ^ J ^ vations in the same position as above, in- 



"^^^^^^^ ^ ^ ."^^^ on V'l'ninv one of the magnets only, or poles 

 — fate and a'. 



( Each result being determined from 5 ob- 

 = 1 17 30 j servations in the same position as above, 



• = 1 17 30 j both magnets being drawn to the ends ; or 



V poles at e and e'. 



In a similar way the following were obtained — 



O / // 



Needle No. 3 — 3 55 23 Mean of 8 observations, poles at a and h' 



— 3 20 0 e and 



142 30 — =— _^'and^ 



= — 4 53 0- 



