Balance or Veetical Force Magnetometer. 



XXXV 



plane, and T is the time of one vibration in a vertical plane.* a e is obtained from 

 the observations in micrometer divisions, one division being = 0'*1003.f 



The time of one vibration in the horizontal plane, T' = 12^-00.| 



Time of vibration in the vertical plane. 



The needle being in its usual position on the agate planes, the moveable wire 

 of the left micrometer is made to bisect the spider-cross ; the needle is then vibrated 

 by means of a small piece of steel, through an angle of about 40 micrometer divi- 

 sions or 4', and the periods of the cross passing the wire, are estimated to a tenth of a 

 second (See Table 12, Introd. 1843, p. xxxix.) The arc of vibration at the com- 

 mencement was measured by means of the right micrometer, it was usually taken 

 very small on account of the difference in the times of vibration with difference of 

 arc (afterwards noticed, 54), although it is now certain that large arcs of vibration 

 give a time which satisfies better the previous equation and the true coefficient of 

 the instrument. 



The following Table contains the observations for the value of T made in 1845 

 and 1846. 



The number of vibrations observed, is given in the column after that contain- 

 ing the arc of vibration at commencement. 



Table 4. — Values of T, the Time of Vibration of the Balance Needle in a Vertical 

 Plane, with the Temperature of the Needle, in 1845 and 1846. 



Gottingen 

 Mean Time. 



Arc at 

 Com- 

 mence- 



Number 



of 

 Vibra- 



Time 

 of one 

 Vibra- 



Tempe- 

 rature 

 of 



Gottingen 

 Mean Time. 



Arc at 

 Com- 

 mence- 



Number 



of 

 Vibra- 



Time 

 of one 

 Vibra- 



Tempe- 

 rature 

 of 







ment. 



tions. 



tion. 



Needle. 









ment. 



tions. 



tion. 



Needle. 



d. h. 

 1845. 



' 





s. 



° 



d. 



1845- 



ii. 



_' 





s. 



° 



Jan. 



1 22 



3-8 



25 



7-14 



34-4 



Mar. 



13 



22 



3-2 



8 



7-08 



31-9 



Jan. 



3 22 



4-5 



20 



7-01 



35-8 



Mar. 



16 



22 



3-8 



15 



6-82 



311 



Jan. 



5 22 



3-6 



25 



8-05 



46-3 



Mar. 



23 



23 



3-9 



15 



8-07 



45-6 



Jan. 



8 22 



3-3 



20 



7-33 



35-9 



Apr. 



1 



11 



4-7 



15 



8-10 



48-8 



Jan. 



13 22 



3-8 



20 



7-53 



38-2 



Apr. 



7 







4-3 



15 



7-90 



47-8 



Jan. 



16 22 



3-2 



15 



7-21 



34-9 



Apr. 



13 



22 



4-3 



25 



7-30 



42-7 



Jan. 



21 



3-1 



25 



7-21 



35-4 



Apr. 



21 



8 



5-1 



20 



8-84 



58-8 



Jan. 



23 23 



4-2 



20 



8-38 



46-2 



Apr. 



21 



23 



3-5 



25 



8-04 



506 



Jan. 



26 22 



3-3 



25 



7-42 



360 



Apr. 



29 







4-1 



25 



7-89 



52-7 



Jan. 



30 2 



31 



25 



6-72 



27-2 



Apr. 



30 



23 



4-0 



15 



8-02 



54-5 



Jan. 



31 2 



3-7 



40 



6-47 



21-5 



May 



4 



21 



30 



15 



7-31 



46-8 



Feb. 



4 22 



3-7 



15 



7-64 



38-7 



May 



7 



23 



4-0 



15 



7-06 



44-7 



Feb. 



12 2 



4-1 



15 



6-93 



32-6 



May 



13 







4-6 



20 



7-56 



50-7 



Feb. 



16 23 



3-7 



20 



7-49 



38-8 



May 



15 



8 



4-0 



15 



8-34 



58-5 



Feb. 



24 



3-5 



20 



7-72 



38-6 



May 



18 



22 



50 



20 



7-56 



50-0 



Mar. 



2 22 



3-9 



20 



7-40 



39-5 



May 



19 



21 



50 



20 



7-37 



48-3 



Mar. 



9 22 



3-9 



20 



7-43 



410 



May 



28 







3-8 



20 



7-11 



47-6 



Mar. 



12 23 



3-6 



20 



6-87 



31-6 



June 



2 



22 



4-0 



25 



7-91 



56-3 



* See Dr Lloyd's Account of tlie Magnetical Observatory of Dublin, p. 38, 



t Introduction, 1843, p. xxxviii. I Introduction, 1841-2, Table 15, p. xxxv. 



