XXXIV 



Introduction. 



Jime 21. 1841. The balance magnetometer was adjusted with the aid of a 

 horizontal needle and Kater's compass, so that the magnet of the instrument 

 should be at ri^ht anales to the maonetic meridian ; the magnet was balanced and 

 its sensibility adjusted by the small screws, and the fixed wires of the microscopes 

 were made to be in the same horizontal plane. 



The crosses of gold wire were found loose, and it was necessary to substitute 

 fibres of silk till July 2, when Mr J. Adie Inserted silver wires. It was not 

 found necessary to readjust the magnet, the bisection of the crosses being sufficiently 

 horizontal. 



July 6. 1841. A difference of ten micrometer divisions was observed between 

 the readings of the two micrometers, due to the line joining the crosses not passing 

 through the centre of motion. 



After July 26. 1841, the north pole of the magnet was towards the east; 

 before that date it was towaids the west. 



40. Determination of the deviation of the line joining the bisection crosses 

 from the magnetic axis. 



For this purpose the needle is reversed on its support ; half the difference of 

 the readings in the two positions is the deviation. 



Table 14. — Observations to determine the deviation of the line joining the Bisection Crosses 

 from the Maffuetic Axis of the Balance Needle. 





July 27. 1841 





July 27. 1S41 





Sept. 1. 1S41 





Oct. 2. 1841. 





Jan. 11. 1842 





N. end 

 of 





















































Needle. 



Mean of 



Mean of 





Mean of 



Mean of 





.lioan of 



Mean of 





! .Mean of 



Mean of 





Mean of 



Mean of 







Two 



AU.M-- 



Diff. 



'I wo 



Alter- 



Dift-. 



Two 



Alter- 



Diff. 



, Two 



A iier- 



Diff. 



Two 



Alter- 



Diff. 





Microm. 



nate Two. 





Microm. 



nate Two 





-Microm. 



nate Two. 





.Microm. 



late 'I'wo. 





Microm. 



nate Two. 





E. 



-195-1 







+ 70-5 







+ 205-6 







-15-0 







-120 







w. 



+ 118-6 



-188-1 



306-7 



+ 370-7 



+ 60-2 



310-5 



+ 190-3 



+ 227-5 



37-2 



-56-5 



-13-7 



42-8 



-236 



- 96 



140 



E. 



-181-1 



+ 100-9 



282-0 



+ 49-9 



+ 356-8 



306-9 



+ 249-3 



+ 173-3 



76-0 



-12-3 



-64 2 



51-9 



- 72 



-239 



167 



W. 



+ 83-1 



-2351 



318--4 



+ 3i30 



+ 46-8 



:i96-2 



+ 15t)-2 



+ 221-5 



65-3 



-71-s 



-23-2 



48-6 



-242 



- 84 



158 



E. 



- 289-0 



+ 27-7 



316-7 



+ .is-s 



+ 3210 



277-2 



+ 193-7 



+ 147-4 



46-3 



-34-2 







- 96 



-227 



131 



W. 



- 27-8 







+ 298-9 



+ 25-5 



27o-4 



+ 13b-5 



+ 184-3 



45-8 









-212 



- 89 



123 



E. 









+ 7-3 







+ 175-0 



+ 137-3 



37-7 









- 83 







AV. 















H- 136-0 



















July 27. 1841. 



Sept. 1. ... 

 Oct. 2. ... 



1st Series, Mean deviation, 153*0 1 Correction for deviation, N. pole 



2d Series, 146*4 J east, + 150 



• • • • 25-7] . 25 



25-11 "^"^ 



Jan. 11. 1842, 72*0 



72 



The first series of observations, July 27. 1841, giving some reason to conclude 

 that the magnet, on reversal, found different bearing points, the supports of the in- 

 strument were examined ; the marble base was found quite level, but the south agate 



